Despite Phantump having one of the highest spawn rates on my example world, it spawns much less frequently than Pineco and Burmy, making getting Ebony leaves a chore after the spawner stops working-- and even before it stops working, as Phantump is not its most common spawn. I can't seem to figure out the cause, but Reviewing the Phantump spawning information may help.

I'm not sure if Pixelmon ever fixed their bug where tags did not work in 'needed nearby blocks.' I will replace the 'minecraft:logs' tag with 'minecraft:dark_oak_logs' and 'minecraft:ebony_logs' and perhaps even w/ apricorn/berry logs, and conduct some other experimentation to see if I can get them to spawn.

Confirmed that 'minecraft:logs' still does not work. Phantump has been modified to spawn around dark oak, ebony, and umbran logs (not apricorn, berry, or others). Fixed for v1.1.3