Won’t allow me to re-enter mobile phone number, any ideas?

Based on the described behavior, the mobile number is most likely being blocked or rate‑limited by Microsoft’s verification system, and repeated recovery attempts are causing additional blocks.

Key points from Microsoft’s guidance and what to do next:

1. Avoid repeated code/verification attempts
   • Excessive or repetitive requests to send verification codes to the same or alternate phone numbers or emails can trigger a temporary or even permanent block on that verification method.
   • Stop trying to re-add or reuse the same number repeatedly for at least 24 hours. Repeated attempts can reset the time lock and make the block last longer.
2. Possible reasons the phone number is rejected
   • Unusual activity or sign-in patterns: Microsoft may interpret this as risky behavior and block sending codes to that number.
   • High volume of requests from your region or “heavy compromised traffic”: this can slow or block code delivery and verification temporarily.
   • VOIP number: VOIP numbers cannot be used for sign-in or verification codes. Only a mobile phone number is supported.
3. Try an alternate verification method (if available)
   • If the sign-in page shows “Try another verification method,” use any other method still associated with the account (backup email, other phone, authenticator app, etc.).
   • If SMS is blocked, using an alternate email that is already on the account is the recommended way to receive a code.
4. Wait out temporary blocks
   • Microsoft explicitly recommends waiting when blocked:
     • Wait at least 24 hours without further attempts.
     • If still blocked, wait longer, up to a week, avoiding repeated sign-in or code requests during that time.
5. If you are not getting codes at all
   • Confirm the number is a true mobile number (not VOIP).
   • Check that the phone is not blocking texts from unknown numbers.
   • If using SMS, ensure the inbox is not full and the messaging app is working.
6. If recovery forms have already been denied
   • When recovery forms are denied multiple times, the only supported path is to:
     • Stop submitting new forms for a while (to avoid further flags/blocks).
     • When trying again later, provide as much accurate information as possible and use any working verification method (such as a backup email) if still available.
   • If no verification method works and forms continue to be denied, Microsoft’s documentation does not provide an additional escalation path beyond waiting out blocks and retrying with correct information.

Because the number was removed and is now being rejected, the most realistic options are:

• Use any remaining verification method (backup email, authenticator) if still offered on sign-in.
• If none are available, stop trying for at least 24 hours (preferably longer), then attempt recovery again with minimal, careful attempts and without repeatedly requesting codes.

References:

• Troubleshoot Microsoft verification code issues
• Common problems with two-step verification for a work or school account
• Can't sign in to my email - Microsoft Q&A
• Azure has blocked myphone number for SMS verification due to a “bad reputation” flag - Microsoft Q&A