The Phoenix Suns confirmed Westphal's death in a statement Saturday. No cause was given, although he had been diagnosed with brain cancer last August.
Born on Nov. 30, 1950, Westphal was a native of Torrance.
In a tweet that included an archival photo of Westphal in his Trojans basketball uniform, USC said: "#FightOnForever, Paul Westphal. Hall of Fame player. Hall of Fame person."
A five-time All-Star guard, Westphal played in the NBA from 1972-84. After winning a championship with the Celtics, he made the finals in 1976 with Phoenix.
He spent 14 seasons with the Suns as a player and a coach.
"Westy will forever be remembered as a prominent Valley sports legend both on and off the court," said Suns Managing Partner Robert Sarver. "He built an illustrious career as both a player and a coach. His legacy ranks among the most quintessential basketball icons of all time."
Westphal also played for Seattle and the New York Knicks.
After his playing career ended, Westphal moved into coaching. He led the Suns to the NBA Finals in 1993, and also was head coach of Seattle and Sacramento. At the college level, he coached at Southwestern Baptist Bible College (now Arizona Christian University), Grand Canyon and Pepperdine.
He was inducted into the Basketball Hall of Fame in 2019.
He is survived by his wife, Cindy, and two children.
The Associated Press contributed to this report.