I'm not up to speed with Phillippe so much, as I tend to stick to the earlier Magma. I guess Phillippe is the guy on the K.A. record and the Mythes et Légendes Epok 1 - 4 albums... He is probably the most conventionally virtuoso (virtuosic?) bassist of the lot...
The classic Magma tone comes from Jannick "Janik" Top. He brought that tone with him. For the Kohntarkosz rehearsal tapes you can hear when Jannick joined the band, as the previous bassist had a much more 'Beatle bass' tone. Jannick's tone came from a Jazz bass, tuned CGDA, into an Ampeg SVT with a master volume added. I guess he drove the preamp section really hard, then lowered the master volume to acceptable levels. On Udu Wudu it sounds like he double-tracks the bass parts as well. He also added octave-down effects and envelope filters.
The freakiest bassist I think Magma had was Bernard Paganotti. This guy had a custom Jacobacci bass with a massive oversized body and three pickups. He lets rip a crazy solo on the Theatre Du Taur Concert, 1975, during MKD. The solo comprises sections of the De Futura basslines and a lot of weird octave fuzz. It sounds like he is using a fuzz like an Arbiter Add-A-Sound, that creates both an octave above and below the original note. He is also using a wah, or possibly a Q filter built into the bass. Crazy stuff.