My company just started requiring Microsoft Intune Company Portal app to use Teams and Outlook. From a friend in IT infosec at another company said the app can push apps, require certain settings, password requirements, or OSs, and can see a lot of stuff on your phone. I don't think this level of intrusion into my personal phone is warranted or ethical. Be warned. I'm just going to uninstall and suffer the internal political consequences.
You are correct. If you were never required to use your personal device before you have the right to fight this. We had something similar here and if people complained they needed to be accommodated. The belief was if we just tell them to do it the majority will and say nothing. It was true, but a handful did not. This wasnt requiring teams or intune though, we have company phones for that. This was requiring the authenticator app fpr MFA for the company. Of course not everyone in the company has a company phone. I would imagine the same applies to this situation.