It's upstairs in T1. IIRC, it's also available in T2 (it gets a little hard for me to keep everything straight). Clear also has the e-gates upstairs in T1.

It's awesome. We used it at PHX last night. We were through security in about 60 seconds total, including bag screening. Add in UA's touchless bag drop option and you have a very smooth, expedited airport experience. I do think T3 PHX is one of the best flying experiences in the country.