Well, the skycaps work for a private company and DL only allows them to do so much. If flying DL out of PHX, I always advise getting there early if you must check bags. It can be a zoo anytime of day. Pre-pandemic, I had a 6pm flight and got there around 4pm. Thankfully, I was flying F, so I could get in the priority line. Still waited 15 minutes! The regular line was easily 1 hour long.