Had you been traveling last night (12/1) you would have mis-connected despite the close proximity of the arrival/departure gates:

Flight # 72
Arrive Phoenix, AZ
Date 12/1/2008
Gate A19
Scheduled 8:35 PM
Actual 10:09 PM

Flight # 1081
Depart Phoenix, AZ
Date 12/1/2008
Gate A14
Scheduled 9:00 PM
Actual 9:22 PM

I would say even the $50 confirmed standby on the earlier flight would be worth it unless you really want to spend the night in PHX. I doubt US would put you up at the Biltmore.