My Dad lives in Phoenix so I have spent a lot of time non-reving out of there. My best advice would be to try and catch that United A320 that goes non-stop PHX-IAD. It leaves at 8am. If you cannot catch that flight, I think Denver is a good connection. When I have been stuck in Denver, the only flight that I can ever get out of Denver on is that DEN-PHX flights. That route is flown by United, US Air, Southwest, and Frontier, so there is always plenty of seats and plenty of flights. Denver and Washington Dulles are both United hubs so there is a ton of flights, many times on widebody jets (767's and 777's). Lots of seats (and jumpseats). You can also go DEN-DCA on United and Frontier, or DEN-BWI on United and Southwest.