#CodersDownUnder/GemsPlusPlus#30
I can't find the generated distribution data for Phoenixite Ore or Nether Phoenixite Ore in the world-gen.json.

Minecraft 1.12.2
JustEnoughResources-1.12.2-0.9.2.60
gemsplusplus-1.12.2-7.0.4
Forge - 14.23.5.2838

Strange since it looks like you scanned a lot. I also don't support 1.12 anymore, but this could also just be a strange coincidence.
Is the ore actually generating (aka can you find any)? Could also just be bad luck that the chunks it checked didn't have any.