Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2018
Mar. 22, 2019
Jun. 29, 2018
Document And Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2018    
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus FY    
Trading Symbol PHIO    
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   22,299,132  
Entity Small Business true    
Entity Emerging Growth false    
Entity Current Reporting Status Yes    
Entity Well Known Seasoned Issuer No    
Entity Voluntary Filer No    
Entity Public Float     $ 8,383,995
Entity Shell Company false    
Entity Former name Rxi Pharmaceuticals Corp.