How is he physically? If he’s not frail, maybe he could do volunteer work: holding preemies in the NICU is one thing older people do.

Maybe let him donate a certain amount to legit charities

Giving money to scammers is fulfilling his need to feel useful and do good. He needs a more productive way to do that.

Also get the phone under control. I know there are special phones for seniors that have ways of blocking scammers.