On the outskirts of downtown I went to a music shop that was attached to a Pawn Shop a few weeks ago that had some nice old Fender amps. I wish I could tell you which one, but I can't. It was next to kind of an artsy little cafe/restaurant that had a delicious tomato and fresh mozzerella sandwich.
I think the one Rotten is talking about is Music Brokers in downtown Phoenix off of 7th street I think, its just OK. Others to look at are Musicans Discount in Mesa and M-Tronics in Mesa which has vintage gear Malinos is across the street but all new gear. Bizzar Guitars is kinda cool but not much used gear.
All and all Phoenix guitar shops aren't great for used gear prices are a bit high and selection is hit or miss.
A great guitar shop in Tuscon AZ is Rainbow Guitars hit that place if you travel south to Tuscon.
I know a guy in Phoenix that has tons of old gear. He advertised on CL last weekend and I went to his house. He must have 12 amps and 20 guitars, almost everything for sale. Old Silvertones, a Yamaha T-50 (soldano), Original Epiphone Amps, lots of Fender, Laney, an Airline amp. Voc cabinets with Wharfdales, etc.
I could PM his name to you if interested. He had guitars, too, but not the Holy Grail stuff - just interesting finds.
I played an Epiphone amp from I think the 60s, made for Gibson in the USA - wow, what an authentic Beatles 60 tone. I bought a Peavey Classic 50 212 that just rocks.