Actually, the very first Mary Coyle's opened 60 years ago at 36th Street and Indian School. They closed in the 60's to open two new locations- at 15th Avenue and Thomas, across from Phoenix College, as well as the one you mentioned north of Bethany Home Road on 19th Avenue. That one eventually closed and only the Thomas Road remained open. That location closed about 20 years ago and they moved to the current location on 7th Avenue, north of Missouri.
Mary Coyle's was retro corny even in the 60's. My family went there to celebrate every graduation. My oldest soda fountain memories go back even farther to Grosso's Chocolates- an Italian chocolatier and ice cream fountain on Washington in downtown Phoenix. It dated back to pre-WWII. I also have fond memories of soda fountain cherry phosphates at Isaac School Drugs (my wife still cracks up at the name) on 35th Ave. & McDowell. I grew up in the area and went to junior high at Isaac. The school dates back to the 20's, had wood floors and was heated with radiators. A real piece of Phoenix history.