Phantom has its uses, no doubt, but I can't imagine just why it possibly needs the serious extent of its drawbacks that it has. The ending lag and the cool-down (being unable to use it for a few seconds) are atrocious, and it's got a rather convolutedly place hitbox in relation to Zelda.
That said, though, it's a fantastic follow-up edgeguarding tool to Dsmash.
About FW, I'm starting to feel as though the final Wii U Zelda build is going to be quite different than the E3 one with regard to knockback percentages (Shoot me if this is so obvious, I've simply never known).
I've seen FW KO at ~100% center-stage in an E3 demo vid, and that's obviously not happening in Smash 3DS.