The method of receiving verification codes via SMS to the linked phone number is not available

Because access to Microsoft Authenticator is lost and SMS verification to the registered phone number is no longer available or fails, the only way to regain access as the sole global administrator is to work with Microsoft support so the Data Protection team can verify identity and reset the authentication methods.

From the provided guidance, the recovery path is:

1. If there is another global administrator in the tenant
   • Ask that admin to sign in to the Azure portal → Microsoft Entra ID → Users → select the locked account → Authentication methods → Require re-register multifactor authentication.
   • After this, sign in again and register new MFA methods (new Authenticator app, SMS, etc.).
2. If there is no other global administrator and this is the only admin account
   • Contact Microsoft support by phone using the regional number listed under Customer service phone numbers - Microsoft Support.
   • In the automated menu, clearly indicate:
     • The issue is with Authenticator.
     • The product is Office 365/Microsoft 365 for business.
     • It is a company account.
     • Confirm being the only administrator.
     • Request creation of a service request with the Data Protection team to recover the tenant admin account and reset MFA.
   • Be prepared to provide tenant and admin details and follow identity‑verification steps.
3. If phone support cannot be reached
   • Create a temporary trial Microsoft 365 tenant from the Microsoft 365 plans page.
   • In that new tenant, go to the Microsoft 365 admin center → Support → Help & support and open a ticket.
   • In the ticket, explain that access to a different existing tenant is lost, provide the locked tenant’s domain and admin UPN, and request escalation to the Data Protection/Tenant Recovery team to reset MFA for the original admin account.
   • After recovery, cancel the trial subscription of the temporary tenant.

Until Microsoft completes this admin recovery, the sign‑in cannot be completed and verification methods (including SMS) cannot be changed.

References:

• Troubleshoot Microsoft verification code issues
• I have a Micrsoft business account and I am the admin and the only user registered under this account. I can't log in because i have replaced my phone and the authenticator doesn't work. - Microsoft Q&A
• Global Admin Locked out - Microsoft Q&A
• I need to reset my mfa methods - Microsoft Q&A
• Requesting a Tenant Admin MFA Reset - Microsoft Q&A
• Common problems with two-step verification for a work or school account