Yes, the former TWA Ambassador's Club is now the Alaska Board Room. That's the only airside clubroom in the entire terminal - CO and DL have theirs landside. 🙁
Interesting, US to T3? AA has an airside Admiral's Club in Terminal 3, but that area is security-shared with United's hub gates.. so if the brain trust in Phoenix was smart enough to cut a full-reciprocal club deal with UA they wouldn't even need to open up a dedicated club - just use the United RCC.