James Rice,
You can change mechanisms for MFA in your online account and update your phone number, and than you can enforce again app mfa setup https://support.microsoft.com/en-us/account-billing/change-your-two-step-verification-method-and-settings-c801d5ad-e0fc-4711-94d5-33ad5d4630f7
If you need, you also can go to recovery scenario options;
- Account recovery form: https://account.live.com/acsr
- Contact Microsoft Support: https://answers.microsoft.com/en-us/msoffice/forum/all/365-account-recovery-without-authenticator-app/e9e5f8e7-6ef4-4a70-b92a-8cc9d5a27f5a
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