If you change your phone, you’ll have to transfer the Microsoft Authenticator 2FA/MFA to the new phone. It is possible to do that on the My Sign-ins site from Microsoft.
If you use Remove you can remove the actual Microsoft Authenticator connection and set up the new phone. But what to do if you want to reset a guest account in another tenant?
You have to change to that tenant – switching to this organisation tenant. You cannot do that in the Security information menu tab – you have to switch to the Organisation tab and change it there.
After switching the organisation, go back to the Security information menu – now you can change the security information for this organisation. Removing the authentication lets you re-register the Microsoft Authenticator App.