All rental counters at PHX are offsite in Rental Car Facility. You need to take a bus shuttle to get there. Hence, 30 minutes is tight but doable if everything runs smoothly. Calling rental counter, even if you can reach someone, will not help. Whatever answer you may receive has nothing to do with whoever may or may not close on time on day of your arrival. I actually had the same issue with PHX where counter was closed when my flight was delayed. I ended up taking taxi to/from hotel for first night and Hertz provided a credit on my rental bill the following day. That was like 10 years ago though.