It's actually less stupid than the state-level bans that allow hands-free devices. Holding the phone isn't the problem; it's the mental distraction caused by talking to someone who doesn't share your environment.

That said, I still oppose this proposal. It's impossible to enforce without invasive hardware and software requirements, and it would inevitably be abused by cops needing to meet their quotas, e.g. ticketing people who are texting or checking maps at red lights.