To be perfectly honest, I've always personally been surprised at what business people are willing to transact over the low-bandwidth media of the telephone. I've heard plenty of stories of people pretending to be celebrities and getting away with stuff on the phone; I don't need a sophisticated computer to do that for me.

If a real problem of deep-fakes in phone conversations emerges, people will just raise the bar of authentication in phone communications. There's nothing magical about telephone that makes it exempt from the general need to protect against social engineering.