Rumor is that Vance Joseph, the supposed leader in the clubhouse for the HC spot, wouldn't retain him.
Phillips is certainly an upgrade over Barry but I don't think he is some grandmaster X's and O's guy who can coach up mediocre talent. Our defense was stocked while he was here, including a future HOF'er in Ware, when he was in Houston he had a guy who may go down as the GOAT DL in Watt if he can stay healthy, and obviously in Denver they are/were loaded at every level of the defense, with yet another future HOF pass-rusher in Miller.
His schemes are usually relatively simple 1-gap, 3-4 stuff, he does a good job of getting production out of interior linemen by freeing them up to rush instead of 2-gap, but overall I feel like he is more talent-dependent than other top coordinators.
Ryan Kerrigan is hardly Ware, Watt or Miller.