Blatant plug here, mods feel free to move it.
There is a bus/travel company now in Phoenix called 'Desert Snow Connection' - the website is desertsnowconnection.com.
They have bus going up to Snowbowl (Flagstaff AZ) from Phoenix almost every day, prices vary between $55 on Thursdays (includes lift ticket) to $85 for weekends and holidays.
For the record, I have no affiliation with them except as a customer.
Mid-week is a pretty good deal, seeing as how a lift ticket alone at Snowbowl is around $50. (Their base lodge, however, recently had some major remodeling and sucks big time).
If you go pack your own breakfast, lunch and dinner. The bus doesn't stop and on-slope dining is expensive, even for this small place.