Subsequent Event	6 Months Ended
Jun. 30, 2023
Subsequent Events [Abstract]
Subsequent Event	9. Subsequent Event On July 14, 2023, the Company completed a voluntary, one-time stock option exchange program, or the Option Exchange, pursuant to which eligible employees were able to exchange certain outstanding stock options granted under Phathom’s 2019 Incentive Award Plan, or the 2019 Plan, for a lesser amount of new restricted stock units issued under the 2019 Plan. Participants in the Option Exchange received one restricted stock unit for every two shares of Phathom common stock underlying the eligible options surrendered. This exchange ratio was applied on a grant by grant basis. The Option Exchange resulted in 2,406,622 options being exchanged for 1,203,341 restricted stock units. The Company is evaluating the accounting impact of the Option Exchange.

The entire disclosure for significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, catastrophic loss, significant foreign exchange rate changes, loans to insiders or affiliates, and transactions not in the ordinary course of business.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 855
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//855/tableOfContent

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 855
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483399/855-10-50-2

Name:	us-gaap_SubsequentEventsTextBlock
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:textBlockItemType
Balance Type:	na
Period Type:	duration