^ Wow, welcome to the forum!
I didn't notice your post before now.
I've been told that generally, the FAA height limit for downtown Phoenix is 500 feet. However, it is logical to assume that the limit goes down as you move east of Central Avenue, closer to the runways at Sky Harbor. Conversely, to the west of Central, the FAA would likely have less of a problem with a 500-700 foot tower, depending on where it is situated.
In addition, I've been told that the FAA cap only extends north as far as Roosevelt Street. I'm not sure if this is true or not.
In addition to the FAA restrictions, the City of Phoenix also has strict height limits. Generally, the entire city is around 56 feet tall, although high-rise zoning exists around much of the downtown and midtown cores along Central Avenue. I think, in Phoenix, anything over 250 feet requires extensive neighborhood meetings and a variance granted by the city. Some areas around the Biltmore have special 140-foot zoning in place.
In other news:
http://forum.skyscraperpage.com/show...threadid=84166
38-story, 480-foot tower proposed for downtown Phoenix
--don