When you're setting up Multifactor Authentication for your TiM Account, you can verify your identity in three possible ways: 1) via the Okta Verify app, 2) by receiving a code via SMS text, and 3) by receiving a code by voice via a phone call.
If you select to verify your identity via SMS text or voice via a phone call, TiM will populate the phone number currently listed in your TiM Profile as the number to receive the code:
If you no longer have access to this phone number or the area is empty, please Contact TiM Support (link here) and submit a request for the phone number registered to your Okta Account to be updated.
You could also request that your Multifactor Authentication enrollment be reset, so you can set up a different method of MFA that does not leverage your phone number, ie: the Okta Verify app. See: How to set up the Okta Verify app