Perception about Wade Phillips as a bad HC, which is not proven, was destroyed by perception of Jason Garrett as a genius, which is not proven. Wade has actually done things. In Buffalo he was a music city miracle away from probably playing for the SB, because he had that defense clicking. And he has in fact been screwed by an interfering FO in that case with the Johnson-Flutie drama.. And he won games with those guys and Buffalo collapsed after he left.
With the Callahan-Garrett saga happening, you can probably get a pretty accurate gage of the politics Garrett must have played during the time Wade was HC, especially during the Dan Reeves debacle.