Phoenix was a city in Arizona. According to some reports, the city disappeared in less than a minute during the Wars of Independence. By 2069, what was once "Phoenix" was being called the "Phoenix Sandbowl", because the Tesla bomb that had destroyed the city had created a huge sinkhole, into which the city fell. According to some, the bomb was the work of "terrorists from the breakaway Southern states". (PROSE: Alien Bodies)
Real world location
Though it's possible that a real world location doesn't exist in the same geographic space in the Doctor Who universe, such cases are few and far between. Thus, the map at right is probably a good indicator of the DWU location of Phoenix, Arizona.