Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	May 03, 2019
Document Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	PHAS
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		28,626,950