It looks like from other posts you don't have ratings yet and looking at atp flight school. I would not worry about getting a Phx base until you have the 1500 hrs. Regional bases open and close all the time. Seniority changes etc. Compass unfortunately doesn't have a Phx base as of April 1.

Skywest and Mesa has been typically senior , same once you can get to a major. Phx is currently nearly impossible to hold brand new with anyone. Luckily commuting out of Phx isn't that bad

Get your time then worry about where to work as nothing is more true then it will change .. for example when I was hired in July reserve was a few months and by the time through training I am looking at an unknown length of reserve ..

We all at compass might not be around by that time hits or earlier