Phoenix served as the state capital of Arizona and had a population of 1.4 million.
Phoenix was the destination of Flight 462. Due to power shortages, the cities airport was no longer functioning and the plane could not land. Jake, while looking out the window, see's large parts of the city going dark. This suggests that Phoenix was in a similar state as Los Angeles. Because of the panic on the ground, Flight 462 was forced to divert to another airport, with San Francisco being mentioned as an alternative. However, due to the FAA grounding all flights and closing all airports, as well as the infected spreading, their were no airports functioning to a degree capable of receiving the flight.
The fate of Phoenix can only be inferred, but it is safe to say it was suffered the same fate as Los Angeles. This would include riots, initially, and then being overrun. Phoenix was not in the list of cities George Geary mentions as having being bombed, so it is possible still standing. One can assume that, in accordance with the initial stage of Operation Cobalt, there are safe zones present in the city. However, until mentioned, the fate of Phoenix is conjecture.