We use Sam's trans very often as he provides very reliable service.  We have recommended this service to many friends coming into PHX.   He has always been dependable--even for last minute pick-up.  Sam is a very sweet, kind, professional man who has picked us up on time every time.  He waits in the cell phone lot at PHX for you and he calls ahead 15-30 min to confirm when he is picking up for transport to PHX.  We used a private service for awhile and were not satisfied.  I found Sam's trans on YELP and have never looked back!