When a phantom spawns through spawners or naturally (via custom biomes through datapacks), they ignore light level completely, while insomnia-induced phantoms use a light level requirement of seven or less. This often results in them spawning and immediately burning up.
They'll also spawn on the ground rather than in the air, but I'm not sure that actually counts as an issue.
To reproduce:
Get a spawner and place it in broad daylight
Use a phantom spawn egg on the spawner
The phantoms will spawn in daylight and immediately catch on fire.
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However, we are already tracking this issue, and this report is a Duplicate of MC-133872, which is a report that has not been resolved yet.
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