I think if that’s the case, I’d get an inexpensive phone with a prepaid plan… and make it clear that it gets turned off if not on call or otherwise pre-arranged.

I’m trying to wrap my head around the CTO writing code unless it was from long ago when they were a developer. If that is the case, the CTO should understand that a better or more performant solution is likely over time. I’d say that was a bullet dodged. That’s very poor executive behavior.