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<!-- Creation Date      : 2020-03-13T15:59:37.9598022+00:00 -->
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  <xsd:element id="phat_FairValueMeasurementsValuationProcessesPercentage" name="FairValueMeasurementsValuationProcessesPercentage" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="phat_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityIssuanceOfConvertiblePromissoryNotes" name="FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityIssuanceOfConvertiblePromissoryNotes" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityExchangeOfConvertiblePromissoryNotes" name="FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityExchangeOfConvertiblePromissoryNotes" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="phat_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityIssuanceOfWarrants" name="FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityIssuanceOfWarrants" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisReclassOfWarrantIntoEquity" name="FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisReclassOfWarrantIntoEquity" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="phat_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisConversionOfConvertiblePromissoryNotesIntoCommonSharesUponInitialPublicOffering" name="FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisConversionOfConvertiblePromissoryNotesIntoCommonSharesUponInitialPublicOffering" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="phat_WarrantsLiabilitiesMember" name="WarrantsLiabilitiesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_IncrementalCommonSharesAttributableToExerciseOfWarrants" name="IncrementalCommonSharesAttributableToExerciseOfWarrants" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_SharesSubjectToRepurchaseMember" name="SharesSubjectToRepurchaseMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_AccruedResearchAndDevelopmentExpenses" name="AccruedResearchAndDevelopmentExpenses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_AccountsPayableAndAccruedExpensesRelatedPartiesCurrent" name="AccountsPayableAndAccruedExpensesRelatedPartiesCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_RelatedPartyTransactionSharedOperatingExpensesDueToTransactionsWithRelatedParty" name="RelatedPartyTransactionSharedOperatingExpensesDueToTransactionsWithRelatedParty" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="phat_PCIPharmaServicesMember" name="PCIPharmaServicesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_ClinicalManufacturingServicesMember" name="ClinicalManufacturingServicesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_MountainFieldLimitedLiabilityCorporationMember" name="MountainFieldLimitedLiabilityCorporationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_TakedaPharmaceuticalCompanyLimitedMember" name="TakedaPharmaceuticalCompanyLimitedMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_RelatedPartyTransactionSharedOperatingExpensesDueFromTransactionsWithRelatedParty" name="RelatedPartyTransactionSharedOperatingExpensesDueFromTransactionsWithRelatedParty" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_AgreementExpirationTermFromDateOfFirstCommercialSale" name="AgreementExpirationTermFromDateOfFirstCommercialSale" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_LicenseAgreementDescription" name="LicenseAgreementDescription" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_CommitmentsAndContingenciesLineItems" name="CommitmentsAndContingenciesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_CommitmentsAndContingenciesTable" name="CommitmentsAndContingenciesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_PaymentForLicenseAmount" name="PaymentForLicenseAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_AdditionalWarrantIssued" name="AdditionalWarrantIssued" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_MaximumAmountPayableInSalesMilestonesUponAchievementOfSpecifiedLevelsOfProductSales" name="MaximumAmountPayableInSalesMilestonesUponAchievementOfSpecifiedLevelsOfProductSales" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_LicenseAgreementTransactionCosts" name="LicenseAgreementTransactionCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="phat_WarrantsExpirationDate" name="WarrantsExpirationDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_FrazierConvertibleNoteFinancingMember" name="FrazierConvertibleNoteFinancingMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_FrazierLifeSciencesIXLimitedPartnerMember" name="FrazierLifeSciencesIXLimitedPartnerMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_NonCashChargeRelatedToFairValueAdjustmentOfConvertibleDebt" name="NonCashChargeRelatedToFairValueAdjustmentOfConvertibleDebt" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="phat_LesseeOperatingLeaseNumberOfOptionToExtend" name="LesseeOperatingLeaseNumberOfOptionToExtend" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_PercentageOfOperatingLeaseAnnualIncreaseInMonthlyRent" name="PercentageOfOperatingLeaseAnnualIncreaseInMonthlyRent" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_OperatingLeaseCommencementDate" name="OperatingLeaseCommencementDate" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_AssetsLesseeAbstract" name="AssetsLesseeAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_LiabilitiesLesseeAbstract" name="LiabilitiesLesseeAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_SupplementalNonCashLeaseInformationAbstract" name="SupplementalNonCashLeaseInformationAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_DebtInstrumentAdditionalBorrowingCapacityAmount" name="DebtInstrumentAdditionalBorrowingCapacityAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_ThresholdProceedsFromIssuanceOfEquitySecuritiesAndSubordinatedDebtToBorrowAdditionalDebt" name="ThresholdProceedsFromIssuanceOfEquitySecuritiesAndSubordinatedDebtToBorrowAdditionalDebt" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="phat_TermLoanMember" name="TermLoanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_LoanAgreementMember" name="LoanAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_DebtInstrumentFinalPaymentFeePercentage" name="DebtInstrumentFinalPaymentFeePercentage" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_DebtInstrumentFinalPaymentFee" name="DebtInstrumentFinalPaymentFee" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_DebtInstrumentPrepaymentFeePercentageOfOutstandingPrincipalAmount" name="DebtInstrumentPrepaymentFeePercentageOfOutstandingPrincipalAmount" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_InterestBearingRateUponCustomaryEvents" name="InterestBearingRateUponCustomaryEvents" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="phat_LenderWarrantsExercisableSharesOfCommonStock" name="LenderWarrantsExercisableSharesOfCommonStock" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="phat_LanderWarrantsExpireTerm" name="LanderWarrantsExpireTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_LanderWarrantsTerminationDate" name="LanderWarrantsTerminationDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_AccruedInterest" name="AccruedInterest" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInNextTwelveMonths" name="LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInNextTwelveMonths" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearTwo" name="LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearTwo" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearThree" name="LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearThree" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearFour" name="LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearFour" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearFive" name="LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearFive" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_LongTermDebtAndInterest" name="LongTermDebtAndInterest" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="phat_DebtInstrumentInterestAndFinalPaymentFee" name="DebtInstrumentInterestAndFinalPaymentFee" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="phat_FoundersMember" name="FoundersMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_EmployeesMember" name="EmployeesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_TwoThousandNineteenEquityIncentivePlanMember" name="TwoThousandNineteenEquityIncentivePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_EmployeeStockPurchasePlanMember" name="EmployeeStockPurchasePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_ShareBasedPaymentArrangementEmployeeAndNonemployeeMember" name="ShareBasedPaymentArrangementEmployeeAndNonemployeeMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_StockRepurchaseProgramNumberOfSharesRightLapse" name="StockRepurchaseProgramNumberOfSharesRightLapse" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="phat_RepurchaseRightLapseRate" name="RepurchaseRightLapseRate" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="phat_RepurchaseRightLapseShares" name="RepurchaseRightLapseShares" type="xbrli:decimalItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="phat_SharesAggregateRepurchasePrice" name="SharesAggregateRepurchasePrice" type="num:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="phat_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestingRestrictionsPlacedOnPreviouslyIssuedShares" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestingRestrictionsPlacedOnPreviouslyIssuedShares" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsSaleOfUnvestedCommonStock" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsSaleOfUnvestedCommonStock" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsIssuanceOfUnvestedRestrictedStockAwards" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsIssuanceOfUnvestedRestrictedStockAwards" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareVesting" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareVesting" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_CommonStockWarrantMember" name="CommonStockWarrantMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_ShareBasedCompensationArrangementByShareBasedPaymentAwardStockOptionsExercisedAndSharesVested" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardStockOptionsExercisedAndSharesVested" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesAndSharesVestedInPeriodWeightedAverageExercisePrice" name="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesAndSharesVestedInPeriodWeightedAverageExercisePrice" type="num:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_IncomeTaxReconciliationPermanentItems" name="IncomeTaxReconciliationPermanentItems" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="phat_IncomeTaxReconciliationChangeInFairValueOfWarrantsAndConvertibleDebt" name="IncomeTaxReconciliationChangeInFairValueOfWarrantsAndConvertibleDebt" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="phat_ResearchAndDevelopmentTaxCreditCarryForwardExpirationYear" name="ResearchAndDevelopmentTaxCreditCarryForwardExpirationYear" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="phat_TermLoanBMember" name="TermLoanBMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="phat_FirstAmendmentMember" name="FirstAmendmentMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
</xsd:schema>
