Is it ok for a CEO to ban your phone from the office?

Wrong question.

In this case the question is “is it ok for a hare brained moron drunk on his own power and perceived importance, to ban a particular phone manufacturer because he’s got a hatred for OpenAi”.

I think we already know the answer to the real question.

A company can do what it wants.

But if a company says I can't bring my phone to work with me, then I'll be finding a new job. That's a bridge too far for me.

A better and more defensible idea is for a company to say "only approved devices are allowed to connect to our network".

By CEO, let’s infer company, although I’m assuming you’re referring to Elon Musk specifically given his recent decision.

Yes, a company can ban devices from the office. Our companies do so in the offices working on sensitive matters. No phones, no devices with wireless capabilities, no cameras, etc.

More commonly, companies will ban unapproved devices from connecting to the company networks, but not their physical presence in the office.

It comes down to how guarded a company wants to be and their specific infosec policies and practices.

That CEO (Musk or anyone else) would need a pretty solid set of reasons for doing so. And vague talk of "privacy concerns" isn't a solid reason. Evidence rather than arguments. But, then again, facts don't seem to matter to some people any more.