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Shareholder Report
 6 Months Ended
May 31, 2025
USD ($)
shares
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name Fidelity Phillips Street Trust
Entity Central Index Key 0000278001
Entity Investment Company Type N-1A
Document Period End Date May 31, 2025
Fidelity Government Cash Reserves  
Shareholder Report [Line Items]  
Fund Name Fidelity® Government Cash Reserves
Class Name Fidelity® Government Cash Reserves
Trading Symbol FDRXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains information about Fidelity® Government Cash Reserves for the period December 1, 2024 to May 31, 2025.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-800-544-8544 or by sending an e-mail to fidfunddocuments@fidelity.com.
Additional Information Phone Number 1-800-544-8544
Additional Information Email fidfunddocuments@fidelity.com
Additional Information Website fundresearch.fidelity.com/prospectus/sec
Expenses [Text Block] What were your Fund costs for the last six months?
(based on hypothetical $10,000 investment)
 
 
 
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
 
Fidelity® Government Cash Reserves 
$ 19 
0.37%
  
Expenses Paid, Amount $ 19
Expense Ratio, Percent 0.37%
Net Assets $ 226,004,428,416
Holdings Count | shares 661
Additional Fund Statistics [Text Block] Key Fund Statistics
(as of May 31, 2025)
 
KEY FACTS 
  
  
Fund Size
$226,004,428,416
  
Number of Holdings
661
  
Holdings [Text Block]   EFFECTIVE MATURITY DIVERSIFICATION (% of Fund's net assets)   Days   1-7 78.4   8-30 3.1   31-60 5.3   61-90 3.5   91-180 3.2   >180 7.4             Repurchase Agreements 52.2 U.S. Government Agency - Debt 35.3 U.S. Treasury Obligations 13.4 ASSET ALLOCATION (% of Fund's net assets)     Repurchase Agreements - 52.2               U.S. Government Agency - Debt - 35.3       U.S. Treasury Obligations - 13.4         Net Other Assets (Liabilities) - (0.9)%