v3.26.3
Document and Entity Information - shares
9 Months Ended
Sep. 30, 2026
Nov. 10, 2026
Cover [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2026  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q3  
Entity Registrant Name Phillip Street BDC LLC  
Entity Central Index Key 0001948368  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer  
Entity Shell Company false  
Entity Small Business false  
Entity Emerging Growth Company true  
Entity File Number 814-01579  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 92-0758632  
Entity Address, Address Line One 200 West Street  
Entity Address, City or Town New York  
Entity Address, State or Province NY  
Entity Address, Postal Zip Code 10282  
City Area Code 312  
Local Phone Number 655-4419  
Document Quarterly Report true  
Document Transition Report false  
Entity Common Stock, Shares Outstanding   29,167,847
Entity Ex Transition Period true