One place that gives a great interline rate is the Wyndham Buttes. The last time I stayed there (in August), they gave me a rate of only $65/night. It's only about 10-15 minutes from the airport and is a lovely hotel. It's winter, though, so the rates may be a bit higher right now. There are a lot of things to do in Phoenix. What are you interested in? Museums? Hiking? Do you want to stay in the valley?