We spoke with Charles at LAX ... and asked whether he agreed with Doc Rivers' son, Austin Rivers, who told us he thought Simmons' Sixers career was over.

And it's safe to say Chuck agrees.

"He's never going to play another game in Philly," Barkley said. "The fans won't forgive him."

"They have to make a trade," he added. "You have to move on from a bad relationship. They're not using him and Joel Embiid has been playing great this year, so they're wasting his talents."

Barkley -- who spent 8 seasons with the Sixers -- is familiar with how ruthless Philly fans can be ... recalling times they were hard on him when he played for the org.

"I know those fans very well," Barkley said. "I thought my name was Charles Barkley Son of a Bitch for a long time when I was there."

CB offered some suggestions on how to end the Simmons saga ... saying Philly needs to hop on the phone and call the Boston Celtics, the Houston Rockets, or the Sacramento Kings to help get a deal done.

Speaking of the Kings, Barkley wasn't too fond of SAC trolling Lakers star Russell Westbrook for his shooting slump the other night ... telling us, "The Sacramento Kings should not be making fun of anybody."