| Cover | Sep. 14, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Sep. 14, 2021 |
| Entity Registrant Name | PhaseBio Pharmaceuticals, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-38697 |
| Entity Tax Identification Number | 03-0375697 |
| Entity Address, Address Line One | 1 Great Valley Parkway |
| Entity Address, Address Line Two | Suite 30 |
| Entity Address, City or Town | Malvern |
| Entity Address, State or Province | PA |
| Entity Address, Postal Zip Code | 19355 |
| City Area Code | 610 |
| Local Phone Number | 981-6500 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.001 per share |
| Trading Symbol | PHAS |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | true |
| Amendment Flag | false |
| Entity Central Index Key | 0001169245 |
