Document and Entity Information - shares
9 Months Ended
Sep. 30, 2019
Nov. 08, 2019
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Trading Symbol PHIO  
Security 12b title Common Stock, par value, $0.0001 per share  
Entity Registrant Name Phio Pharmaceuticals Corp.  
Entity Central Index Key 0001533040  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer  
Entity Common Stock, Shares Outstanding   26,404,670
Entity Small Business true  
Entity Emerging Growth false  
Entity File Number 001-36304  
Entity Interactive Data Current Yes  
Entity Incorporation Country Code DE  
Entity Current Reporting Status Yes