Michael Phelps -- I Partied with My Other Medals Too!

All that glitters is not gold ... sometimes it's silver too -- and Michael Phelps partied with BOTH last night in London, hitting up a nightclub with his 2 silver medals from the 2012 Games ... in addition to his 4 gold.

As we reported, Phelps hit the party scene in Soho with his gold medals -- but turns out ... Phelps is an equal opportunity boaster ... bringing out his silver medals too.

Dude's got more hardware than Home Depot.