You can ask the admin to reset the 2FA authentication method to use MS Authenticator app instead of using a mobile number because as per my personal experience cellular networks sometimes have trouble delivering SMS: https://answers.microsoft.com/en-us/msoffice/forum/msoffice_o365admin-mso_password-mso_o365b/reset-2fa-for-office-365-account/caec62dc-3603-4a3d-9670-01b1ddc3e519
After you have successfully regained access to your account & you want to replace the verification method on your own then you can visit this link: https://mysignins.microsoft.com/security-info
I hope this answers your question.
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