Debt - Schedule of Future Minimum Principal and Interest Payments Under Term Loans (Details) $ in Thousands	Sep. 30, 2021 USD ($)
Debt Disclosure [Abstract]
2021	$ 1,625
2022	5,720
2023	5,918
2024	21,040
2025	50,912
2026	62,705
Total principal and interest payments	147,920
Less interest, PIK interest and final payment fee	(47,920)
Total term loan aggregate principal amount	$ 100,000

Debt instrument interest and final payment fee.

No definition available.

Name:	phat_DebtInstrumentInterestAndFinalPaymentFee
Namespace Prefix:	phat_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Long term debt and interest.

+ References

No definition available.

+ Details

Name:	phat_LongTermDebtAndInterest
Namespace Prefix:	phat_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long term debt maturities repayments of principal and interest, year one.

+ References

No definition available.

+ Details

Name:	phat_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestDueNextTwelveMonths
Namespace Prefix:	phat_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long term debt maturities repayments of principal and interest in year five.

+ References

No definition available.

+ Details

Name:	phat_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearFive
Namespace Prefix:	phat_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long term debt maturities repayments of principal and interest in year four.

+ References

No definition available.

+ Details

Name:	phat_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearFour
Namespace Prefix:	phat_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long term debt maturities repayments of principal and interest in year three.

+ References

No definition available.

+ Details

Name:	phat_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearThree
Namespace Prefix:	phat_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long term debt maturities repayments of principal and interest in year two.

+ References

No definition available.

+ Details

Name:	phat_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestInYearTwo
Namespace Prefix:	phat_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long term debt maturities repayments of principal and interest remainder of fiscal year.

+ References

No definition available.

+ Details

Name:	phat_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestRemainderOfFiscalYear
Namespace Prefix:	phat_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_DebtDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant