Their personalities and back-stories are different; they have different looks, different clothing style (well, at least until CC left Excalibur and Davis put Rachel in the original Phoenix costume) they even manifested and used "Phoenix" differently (Jean always used the claws and Rachel the wings, I also liked how most times Rachel's Phoenix-effect wasn't drawn with a head and her hair would light up instead and her tattoos would get stretched to the sides.) But what's the point of spending another word on this subject? ;) You obviously don't want Rachel back (at least not as Phoenix) and nothing would change that, right? :)