I've been reading Avengers VS X-Men and I'm trying to understand when the Phoenix Force went over the edge. During the Dark Phoenix saga, the Phoenix was tainted by Jean's emotions and Mastermind's manipulations. Since then, the Phoenix has had several hosts, mostly Jean and relatives, but wasn't a planet killing nut that makes Galactus look like a kitten.
Did I miss something somewhere?
Also, when these cosmic entities go crazy don't the other cosmic entities usually step in to get things in check?