I think you missed the point. The process creates an identifier, by strongly associating you with the phone number.
This association allows the bank to quickly establish your identity later when you call up or use online services.
Come on guys. It’s obvious why banks have this. Everything identity related is stolen constantly.
1. It is quite easily to accidentally take over someone's account(s) on various mobile apps when you get a new phone number these days. Many apps will allow you to log in with your phone number, reset password or do one-time login via SMS, etc. Some even do it automatically as a convenience. This isn't an edge case issue -- this happens on several of the top social media platforms, etc.
2. SIM swapping is still a viable fraud vector for identity theft and financial crime.
3. It is very vulnerable to phishing, and its prevalence only has exacerbated that.