Expect encryption like RCS and WhatsApp to go away by popular demand, because when phishing gets too good, the only solution will be a service like Google recording all telephone calls.
The logical solution will be, we need a service that scans all calls for phishing, just like we have for email. The service cannot be local for the same reason as for email.
Come on, we have been using encryption, one-time codes, recovery codes for over a decade. I don't see that as the logical next step. Just make addresses renewable tokens that prove that you are allowed to contact some underlying number.
tel:+56 1234 5678::[$SEED/TOKEN THAT SUPPORT K_TIMES_USE+EXPIRATION FROM A FIXED CALLER/SENDER]
My phone will double check the token and ignore things when the calling tokens were used, expired, abused somehow and maybe kindly let you know if no human gets to see your call/text/media or maybe reporting the sender for abuse in case it's something that may be prosecuted according to local law.
Want to support calls from unknown numbers? Sure, wire me crypto with some secret and call me using that. If it wasn't worth my time at least I'll enjoy a beer.
Voice cloning will get to the point where it's so good that there's no tech-savvy users who can detect it the way they can for email. Users will demand for protection to be added to their calls because you really can't live without it.