The Insomnia Temple.

It appears when the phantoms are trying to put you to sleep, but you kill them. It shows how they're just bothered by the insomnia energy, and they build something to bribe you to sleep. If you don't sleep, you're a heartless murderer.

The phantom's eyes would contain shulker boxes (already loot) that contain loot tables. There would be stuff like their drops, presents, and other things. They even give you a pillow.

Phantoms spawn around the temple a ton in regular conditions, and a burnless one occasionally pops out at day.

Have fun - and DON'T make a phantom farm out of it!