For people unfamiliar with PHX Terminal 4, meeting at the Paradise Bakery restaurant in the central food court on the departure/arrivals Gates Level 3 is a good option. There are slightly more comfortable chairs in the hallway/walkway between the food court and the security checkpoints for the WN gates. I think meeting at either of these areas is preferable to trying to find each other at a car rental counter. You have a better chance of finding a chair on the Gates Level 3.

CO used to be in Terminal 3 many years ago, then moved to Terminal 4, and maybe 2 years ago moved to Terminal 2. Definite downgrade going from Terminal 4 to 2.