HP656 was 20 minutes early today at gate A20. HP454 is leaving out of gate A13, the next concourse over. 45 minutes is plenty of time if the flight arrives on time.

Terminal 4 map: http://phoenix.gov/AVIATION/support_...rectoryweb.pdf

There are two flights to SLC after that one but it looks like they are pretty full. Even so, if you have just 10 minutes and make the flight, your luggage still has a way to get up to SLC on the same night.