No phone number to call for Alaska. Just show up. If you are trying to jump on a flight that is a commuter flight or a full flight; try to get there an hour prior to push. It's first come first serve for all offline pilots. If not and the flight has seats, no later than 30 minutes prior. Seems we board very early nowadays.
If it were me, I'd try to be there 1 hour prior !

Cheers !