Well, first I might mention to check out the league locator and the tournament locator on the Pokemon Organized Play website. However since I am bored right now.
One League in Phoenix on Saturdays: Location: atomic comics / phoenix-metro Address: 10215 n. 28th drive #a-1 City: phoenix State: Arizona Postal Code: 85051 Country: United States League Phone: (602) 395-1066
As for tournaments there appears to be none for your specified time of visit.