We have flown America West and now U S Airways from Sacramento to Mexico with a return stop and customs in PHX several times and a couple of times it was during the Thanksgiving holiday period.
We did not have any lengthy delays and it went fairly fast. It is MUCH better than LAX and more comparable to SFO. Providing your flight is on time, the time you have between flights (1:45) should be more than sufficent.
We did miss our connecting flight out of PHX once, but that was only because of major delays on our 1st flight out of Cancun. We were thru customs in about 20 minutes on that occasion.
As with most airports, be ready for a long walk.