Debt - Schedule of Future Minimum Principal and Interest Payments Under Term Loans (Details) $ in Thousands	Sep. 30, 2020 USD ($)
Debt Disclosure [Abstract]
2020	$ 916
2021	13,219
2022	19,065
2023	17,840
2024	11,198
Total principal and interest payments	62,238
Less interest and final payment fee	(12,238)
Total term loan borrowings	$ 50,000

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

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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

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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

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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

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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=120520924&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

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