I agree with @Libb@piefed.social. I would not mix the two at all. If they want me to have a phone with their apps on it, they can provide me one.
Also, for your privacy, it may not be actually the best idea to switch back to a dumb phone, because then you are limited to SMS, which is not secure, and phone calls, which are not secure.
On a smartphone you have things like signal.