Can't tell you much about ATAX or Guidon Philippe, but they were common on French bikes of the period.
I can tell you it's not a PX-10 - the "Aztec" lugwork, which is what I think I can see in your photos, was common on lower-end Pugs, including the ubiquitous UO8. PX10s had Nervex lugs, either plain, or the prettier "Professional".
There are few French bike enthusiasts that regularly post here, so I'm sure one of the them will be able to tell you more about the bars and stem.