Normally, I'd say drive and see America if you have not taken a real cross-country trip from sea to shining sea (or at least part of it).

However, it sounds like you need to calculate the miles on the car because of the lease, plus food and lodging. You'll have to run the numbers and see what is most cost effective. Just remember that Phoenix is really spread out. So you'll probaby be putting more miles on your car there than you planned for.