I got my parents a call blocking box that has a big red button. If they get a robocall they just push the button and the number is blocked. It's dramatically cut down on the amount of junk calls they get. They too are a lot less likely to answer a call from a number they don't recognize, letting it go to the answering machine where if it's a legit call they can just pick up and interrupt the machine.

Answering machines - how quaint (yet effective for call screening!)