Phantoms an End-game mob

Phantom should be an End dimension hazard which makes traversing its islands an endgame challenge and obtaining elytra a true reward.

Nether has a flying enemy, so why end shouldn't?

The concept of Phantom as a punishment for not sleeping enough should be thrown away. Instead, Phantoms spawn like normal mobs.

Conditions for spawning:

Spawn block is any airblock, and, it has to have direct sight of sky and the void, and, it cannot be lower than 200y, and, Rare spawn chance

Behaviour:

Stalking: When Phantom spots a player it starts circling above it in a safe distance

Attacking: When certain conditions are met, the Phantom attacks by swooping down and retreating till conditions are met again

Fleeing: Phantom flees if the player has an elytra equipped

Conditions for attacking:

Player stands on one block wide or one block high bridge with void below, or, Player has less than (number of stalking Phantoms × 2) hearts, or, Player has the levitation effect, or, Player has no blocks below it, and, Player does not have elytra quipped

Optional:

At night, Phantoms rapidly spawn around stronghold in the sky. While in the overworld, Phantoms are hostile to all passive mobs.

Optional: Phantoms are the only entity in Minecraft immune to void damage, as they feed on prey they push off.

This makes Phantoms a serious consideration while traversing the End, while being manageable when on full health and prepared. And not a problem post-game.