Any continuous effects with a “for as long as” duration ignore phased-out objects. If ignoring those objects causes the effect’s conditions to no longer be met, the duration will expire.

No player can cast spells or activate abilities in between the modes of a resolving spell. Any abilities that trigger won’t be put onto the stack until Unite the Coalition is done resolving.

As a permanent is phased out, Auras and Equipment attached to it also phase out at the same time. Those Auras and Equipment will phase in at the same time that creature does, and they’ll phase in still attached to that permanent.

Phasing out doesn’t cause any “leaves the battlefield” abilities to trigger. Similarly, phasing in won’t cause any “enters the battlefield” abilities to trigger.

If Unite the Coalition is copied, the effect that creates the copy may allow you to choose new targets, but you can’t choose new modes.

Phased-out permanents are treated as though they don’t exist. They can’t be the targets of spells or abilities, their static abilities have no effect on the game, their triggered abilities can’t trigger, they can’t attack or block, and so on.

If you choose any mode more than once, you choose the relative order of each of those modes.

An attacking or blocking creature that phases out is removed from combat.

Choices made for permanents as they entered the battlefield are remembered when they phase in.

Permanents phase back in during their controller’s untap step, immediately before that player untaps their permanents. Creatures that phase in this way are able to attack and pay a cost of during that turn. If a permanent had counters on it when it phased out, it will have those counters when it phases back in.

No matter which combination of modes you choose, you always follow the instructions in the order they are written.