Thanks everyone - it was a weird schedule change. They pushed out the departure by :32, but the arrival in PHX was only pushed out by :17. So, I guess they expected to become 15 minutes more efficient somehow. I never accepted it but didn't fight it because the change was so small.
I can't jump on an earlier PHX flight so the alternative would be getting to LAX for the PHX flight or just flying nonstop from LAX.
It's an American Eagle flight and the aircraft is making multiple flights throughout the day. I take this flight pretty regularly so sometimes they do have enough slack in the system that they can make up delays. However, if it's earlier in the day and the aircraft is very delayed, I'm going to start calling AA even if they haven't already announced the delay on my segment.