I'm quite sure almost any game(including FF:T) that uses magic uses this, except, they usually don't set it up that you have to be extra-carefull with your mana.
When running out of mana, mana-abilities(spells) become unavailable and characters have to use less effective attacks/actions.(hitting the opponent with your wand while not wearing any armor)

Okay, that makes sense. For some reason, I was thinking that you were saying that, in most games, mana was necessary for any action, including movement and things like that.

There are a few games out there that use fuel(and usually ammunition as well) as a resource, and include some kind of supply-unit(s).

The phase approach is more simple and more easily comprehended, although i feel that if you wish to.approach this on a tactical level specifically then it may not be idea. The action point method allows for more freedom and development on the field. But why not create your own hybrid. Innovation has never hurt anyone.

I think an action point system works well. Especially if you allow enough action points to accomplish more than one phase.

For example I will use an artillery unit.

Artillery: 10 ap

Move: 5 ap

Set up: 5 ap

Attack:5 ap

Pack up: 5 ap

That way you have more combinations than just being able to perform one action per turn.