Excalibur was more or less happening in its own universe, ignoring everything else (even phone lines and post office obviously). Maybe that reflect how american think about england (or the reverse)
Anyway, it discard that it was stated several time that Jean was the first being contacted by the Phoenix. Whatever Jean was possessed (host) of the Phoenix or a copy created by it, the explanation was that it purpose was corrupted by the limitation of being incarnated into a mortal. It found itself trapped and forgot who/what it was and thought it was only Jean Grey.
If it wasn't the first time that the Phoenix took a mortal host, it should have know what to expect and should have avoided doing the same mistake again. But authors just want to use the Phoenix concept as they see it and don't care about consistency or what was writen previously.