Fix the phone system so calls must positively identify themselves.
There is no reason anyone purporting to be from a business or the government should be able to place a call without cryptographically proving their identity.
I like that! I’m sure it would take a little bit of time for folks to stop trusting calls from personal numbers where highly-capable social engineers do their best work, but eventually I expect nearly all of us would learn the lesson.
And presumably we could set up notifications so our elderly relatives’ phones would alert us to calls from unverified numbers not in their contact list lasting longer than a minute or two.
There is no reason anyone purporting to be from a business or the government should be able to place a call without cryptographically proving their identity.