You can hardly teach a large part of the population how to drive a car and use the indicators when switching lanes. How can you expect to be able to teach them security processes?

The only working approach would be to make a law that phone companies must ensure that caller numbers cannot be spoofed in any way and make them responsible for loses due to spoofed numbers.

And require that banks publish which phone numbers they call customers from (like spf is for email), and do so in a format that mobiles can use. So the mobile can show the customer "this is really your bank" or "unknown caller".