The Utah approach was specifically agreed upon by users local to that community. For a number of reasons, mapping the grid system in Maricopa County does not lend itself as well to the approach taken in Utah. The on-the-ground rule is just as much "how the locals refer to it" as it is "what the street signs say." Have you considered why so many of the streets you've updated have had the prefix for 15 years, and why within that time no other users have attempted to remove them? I also agree that you should revert all your edits to remove prefixes to Phoenix area streets or at least bring this to the community forum so you can get perspective from local users.