While playing in a buffet world set to end generation I noticed that no phantoms were spawning after not sleeping in a bed for about 4 hours.

I created another world and modified the JSON stats file to artificially increase my time since last rest to over 2 years and still did not get any spawns. I also made sure I was above sea level and had no blocks above me.

I created a platform above the void to prevent other mobs from spawning and impacting the mob cap. Then I turned off the day cycle during the night time so it was always possible for phantoms to spawn.

Still no phantoms spawned.

I used an NBT editor to modify the level.day file so the world generation was set to "chunk_generator":

{"type":"minecraft:overworld"}

instead of "chunk_generator":

{"type":"minecraft:the_end"}

. After starting Minecraft again, phantoms started spawning almost instantly and continued to spawn every couple of minutes.

I used the NBT editor to change the world generation back to "chunk_generator":

{"type":"minecraft:the_end"}

and phantoms stopped spawning. Nothing else was changed or modified. Changing back to "chunk_generator":

{"type":"minecraft:overworld"}

had phantoms spawning again.

Phantoms should spawn in the over world regardless of the chunk_generator value.