It seems that you need to configure your accounts in the Authenticator app on your new iPhone. If you're signed in on your computer, follow these steps:
Access Your Security Info: Go to https://mysignins.microsoft.com/security-info and sign in with your account.
Remove and Re-add the MFA Method: Under your security info, you’ll see your registered MFA methods (such as the mobile app for notifications). Remove the existing MFA method, then click Add method to set up your new device or update your settings.
OR
If you have access to Entra ID in the Azure portal, navigate to Azure Active Directory > Users. Select the user who needs to reset their MFA settings, and then look for options like Authentication methods or Multi-Factor Authentication settings in the user's profile.