Changing between multiple Microsoft Teams accounts within the app or browser
If you've changed to a new phone, the most common reason is that the Microsoft Authenticator app was not transferred with your account information, so it can no longer approve sign-ins.
Since this is a work or school account, if the Authenticator app on your old phone was your only available MFA method, you will need to contact your organization's IT administrator and ask them to reset your MFA/security authentication methods. You can refer your administrator to this guide: Manage authentication methods for Microsoft Entra multifactor authentication - Microsoft Entra ID |…
If you’re unsure who your IT administrator is, see How do I find my Microsoft 365 admin? - Microsoft Support
After the MFA methods are reset, you should be able to sign in and register your new phone or Microsoft Authenticator as the new verification method by visiting My Sign-Ins | Security Info | Microsoft.com page.
To help avoid this issue in the future, please refer to the following steps to reconfigure MFA on a new phone:
-Visit the My Sign-Ins | Security Info | Microsoft.com page to manage your verification methods
-Sign in with your work account.
-Select Add sign‑in method > Microsoft Authenticator.
-Install Microsoft Authenticator on the new phone.
-In the app, choose Work or school account, then scan the QR code shown on the Security Info page.
-Approve the test notification sent to the new phone.
-Once the new phone works, remove the old device from the Security Info page.
I hope this information is helpful.