Proposed resolution:

This wording is relative to N5001.

1. Modify [rand.synopsis], header <random> synopsis, as indicated:

   […]
   // [rand.eng.philox], class template philox_engine
   template<class UIntType, size_t w, size_t n, size_t r, UIntType... consts>
     class philox_engine;               // partially freestanding
   
   […]
   using philox4x32 = see below; // freestanding
   using philox4x64 = see below; // freestanding
   […]
   

2. Modify [rand.eng.philox], class template `philox_engine` synopsis, as indicated:

   namespace std {
     template<class UIntType, size_t w, size_t n, size_t r, UIntType... consts>
     class philox_engine {
       […]  
       // inserters and extractors
       template<class charT, class traits>
         friend basic_ostream<charT, traits>&
           operator<<(basic_ostream<charT, traits>& os, const philox_engine& x); // hosted
       template<class charT, class traits>
         friend basic_istream<charT, traits>&
           operator>>(basic_istream<charT, traits>& is, philox_engine& x);       // hosted
     };
   }
   

Philox engines don't seem to require floating-point operations or support from the operating system, so they are probably suitable for freestanding. However, as P2976R1 was finished before the adoption of P2075R6, these engines are not made freestanding yet.