If you are able, you can change your verification option to something other than the SMS code (https://aka.ms/mfasetup).
Otherwise if you are the only global admin for the tenant and are locked out, you will need to reach out to the Azure Data Protection team to get unlocked. Azure Data Protection number: (866-807-5850)
That team will only support you if there are no other global admins on the account. Otherwise, they'll recommend that one of the other admins changes your verification option and lets you back in.