Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2020	May 07, 2020
Document Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Entity Registrant Name	PhaseBio Pharmaceuticals Inc
Entity Central Index Key	0001169245
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock Shares Outstanding		28,781,044
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes