I think it should be pointed out that the basic reason that the non-commercial sector of the FM band in Phoenix has mostly religious occupants is because no other noncommercial operation came forward to get these frequencies when they were available. This was not true in Los Angeles, San Francisco, or even your own San Diego (although the last one is a special case that I'll get to in a moment.)
When I first visited Phoenix in July of 1971, KMCR (91.5 mHz, now KJZZ) was just getting off the ground. As far as I knew for many years (I later found out I was wrong), that was Phoenix' first noncommercial outlet. The next one didn't appear until KFLR (1979 or 1980, if memory serves) at 90.3 mHz. Then came KBAQ at 89.5 in the mid-1980s (it was a joint partnership between Arizona State University and the state of Arizona) followed in the early 1990s by the shared stations at 88.3 of KPHF (religious) and KNAI (Radio Campesina) (the years are per my memory and therefore may be wrong). By the late 1990s and early 2000s, you had K-Love on89.9 mHz (licensed to Superior) and also on 90.9 (licensed to Prescott but which puts a fair signal into north central Phoenix where I live.)
Let's compare that with Los Angeles. When I finally moved from Tujunga to Phoenix in 1972, the Los Angeles noncommercial dial was pretty much set with (going backwards in frequency) KUSC at 91.5 mHz; KPFK at 90.7 mHz; KCRW at 89.9 mHz; KPCC at 89.3 mHz; KXLU (which could not be heard much outside of west Los Angeles) at 88.9 mHz; KCSN in Northridge at 88.5 mHz (it was the last to come on the air in my area); and Long Beach's KLON at 88.1. Because these (mostly) college and university stations had gotten there first, there was very little (if any) room for religious outlets to enter the noncommercial section of the FM band in that city.
I said above that San Diego was a special case. The reason is that the California city sits directly across the border from Tijuana, meaning that the available FM frequencies had to be shared between U.S. and Mexican-based stations. Further murkiing up the waters is the fact that frequencies between 88.1 and 91.9 mHz are *not* considered to be noncommercial frequencies by the Mexican government. The result is that, though there are only two U.S.-based noncommercial radio stations over there (three if you count the on-again, off-again licensed to Descanso at 89.1 mHz), U.S. religious outlets have never been able to get their foot in the door in the noncommercial band there.
And that is my point. The primary reason that religious stations now dominate the noncommercial sector of the FM band today in cities like Phoenix is because when that part of the band was wide open, few, if any, secular noncommercial entities chose to apply for radio stations in the band.