PHX was a hub way before that. For HP (America West), it was the major of 2-3 hubs (others being LAS, and for a while CMH). When I lived in Arizona (1995 to 2015) it was certainly a hub for an airline the entire time.

As for the airport... There have been changes/upgrades to the terminals. Terminal 1 was gone by the time I got to AZ; Terminal 2 had definitely seen better days, and was eventually demolished as well. Terminal 3 has been about doubled in size, to accommodate the airlines that had been in T2.
That leaves T4... The first time I went there (Dec 1995 I think), it seemed nice and new, spacious, great restaurants, etc. HP, then US, and now AA always had 4 concourses of T4. WN had only 2, then they paid to expand and add a 3rd concourse, and a 4th. HP/US/AA simply hasn't paid to upgrade T4 @ PHX like other airlines have (some airlines helped fund the renovations in T3).

I don't understand the comment on, "tiny clubs." Yes, there is one very small lounge (the high As), but the low A and low B lounges are both rather large. The new one was something else (I can't remember what, concessions maybe?), and HP/US created a lounge there (around the time of that merger) since there was no lounge in that part of the airport. It drew complaints almost immediately for being too small.

I've connected at PHX several times (including once for a mileage run when I lived in AZ). So long as you have a proper connection time (45 minutes or greater), you shouldn't have any issues.