Number, I'm on Panniccia's twitter now and I don't see where he says she's not using the Phoenix codename. Can you provide a direct link?
Number 2, since everyone knows her as Jean Grey for so long, people often call her Jean Grey. During the Morrison run and in Endsong, she was clearly Phoenix, yet most of the time people just called her Jean.
Lastly, what artists say doesn't really matter. For years, and even as early as early this year they jumped up and down claiming teen Jean was the only Jean we'd get. Clearly that's not true, and it's not like they got out of their way to tell fans all the stories in the future. If they would honestly leak out everything that was going to happen, why would we buy the comics in the first place?
A lot of the stuff you're upset about is your imagination running wild. If something is actually published and you don't like it, fine. But there's no reason to come out with wild doomsday scenarios.
You like the character Jean Grey, just be happy Adult Jean Grey is back and see where the stories take us.
I will say that since her return is time at the same time as the X-Men movie Dark Phoenix, I seriously doubt she won't be Phoenix. The series about her return is titled PHOENIX: RESURRECTION.