MTGNexus

Will this phase in onto the battlefield or still in the graveyard?

Card Name (Uncommon)
2WW
Creature — Type
Flying
5WW: Card Name phases out. Activate this ability only if Card Name is in your graveyard.

Only permanents can phase in.

Generally my reading of phasing only permanents can phase out too so you'd probably need rules update to allow it but it's likely if they implemented this it would be basically if a card phases out from a location other than the battlefield it would become a phased out permanent (or simply not be allowed if it's a non permanent card).

There is a material distinction between entering then phasing out since it generates triggers so I find it fairly mechanically interesting and it seems like something that could be done.

Neither. The ability effectively does nothing since phasing only works with Permanents and a card in the graveyard is not a permanent. You would have to add something that says "Card Name returns to the battlefield phased out" if you want it on the field. There is not situation where something can be phased out if it isn't on the battlefield.

702.26d The phasing event doesn't actually cause a permanent to change zones...

Bah! But yeah, it makes sense. It's what makes phasing unique, I guess. There's already effects that do what I want. I just got caught up in the flavor. (If you could see the whole card, you'd know what I mean.)