You basically came up with something similar to my thoughts, Dane, which was making Phasing an environment-only power (with the caveats as your description does about letting you make phased projectiles and the like) and then POSSIBLY making a separate 'Invulnerability' power (which could be utilised in conjunction with Phasing) for limited bouts of total invulnerability to all attacks. Right now I'm leaning towards "let people make up their own versions of that through moves", but it merits some personal thought. Any further ideas I have, I'll put in The Loft (since I like to keep granular discussion of systems implementation as part of a smaller team, rather than a wide-open forum).
Curious about me and the characters I play? See the 'Staff' page! See also the rosters for my characters Samus Aran or Enel if you'd like to see examples of well-formatted rosters. Hope you enjoy the Omniverse!