Primo is a wonderful restaurant, no doubt about that. I'm not sure it's worth the drive down from Phoenix, though, all on it's own. Make a weekend of it, and visit Poca Cosa and Janos, and it might be worth while.
I agree with Booklegger: it's got some great dishes but is not a destination restaurant. However, their onion foccacia and zeppole are the best I've had anywhere, and sometimes I dream about them between visits to Tucson.