This bird does not seem to have white outer tail feathers or a whitish tail tip, therefore not a Western or Cassin's Kingbird? Also, I don't think Cassin's is supposed to be in Phoenix.
Could it be a Tropical or Couch's Kingbird? Much more likely Tropical based on range. If so, a good bird for Phoenix, I think. Perhaps the bill is not robust enough for either of these, but perhaps that is because of the angle.
Definitely a kingbird.