I disagree and would not use Flagstaff as your base. Flagstaff is a "ho hum" sleepy little town.
I'd use Sedona which has a lot more to do and prettier views. There are many hotels there at various prices. You didn't provide a price range - everything from moderate to luxury. Many things to do in Sedona including pink jeep tours, trolley orientation rides, hiking, Slide Rock, shopping, etc. Do an internet search.
Phoenix - eat at Cooperstown and Hardrock Cafe downtown. Top three tourist attractions are Heard Museum on Central Avenue, Desert Botanical Garden,and Taliesin West (designed by Frank Lloyd Wright). You could out to Tempe and see ASU, hang out on Mill Avenue where there are many restaurants and bars and see Tempe Town Lake. You didn't mention an age group so it makes it hard to know what might interest you.
visited Sedona and Grand Canyon numerous times.