Accounts payable and accrued expenses related parties current.

No definition available.

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

- Definition

Related party transaction shared operating expenses due from transactions with related party.

+ References

No definition available.

+ Details

Name:	phat_RelatedPartyTransactionSharedOperatingExpensesDueFromTransactionsWithRelatedParty
Namespace Prefix:	phat_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Related party transaction shared operating expenses due to transactions with related party.

+ References

No definition available.

+ Details

Name:	phat_RelatedPartyTransactionSharedOperatingExpensesDueToTransactionsWithRelatedParty
Namespace Prefix:	phat_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

+ Details

Name:	us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_PrincipalOwnerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=phat_PCIPharmaServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=phat_ClinicalManufacturingServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=phat_MountainFieldLimitedLiabilityCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=phat_TakedaPharmaceuticalCompanyLimitedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=phat_TakedaLicenseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Related Party Transactions - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Frazier
Related Party Transaction [Line Items]
Outstanding accounts payable and accrued expenses	$ 40,000		$ 100,000
Shared operating expenses	43,000	$ 60,000
PCI Pharma Services \| Clinical Manufacturing Services
Related Party Transaction [Line Items]
Outstanding accounts payable and accrued expenses	200,000		300,000
Expense related to services	400,000
Mountain Field LLC
Related Party Transaction [Line Items]
Shared operating expenses	0	$ 100,000
Takeda \| Takeda License
Related Party Transaction [Line Items]
Outstanding accounts payable and accrued expenses	22,000		$ 100,000
Expense related to services	$ 0