I'm not really an expert, but Phil's sound can be divided into several phases - early on he's pictured with a Jazz Bass, also a Gibson EB (O or 3, can't remember!). Then he starts using Guild Starfires, maybe concurrently with Jack Casady. Those get modified by Alembic, then Alembic starts building instruments for them. (The Gibson gets the mod treatment too - Bi Sonics and custom electronics.) Late-'70s he starts using a bass built by Doug Irwin, and at some point after that he moves over to Modulus (with a few stops along the way). In recent years he started using a Ritter, though he seems to still switch between that and the Modulus's (Moduli?).
I think many people prefer the Guild/Alembic phase - here's a video with some nice shots and the sound is pretty decent. Equipment-wise, it's the Alembic-modded Starfire, with flats played with a pick: