For security purposes, we use phone verification as one of the methods to help verify a user's identity on the site. The error probably means the phone carrier (company) that the phone number belongs to is not supported.
If you have another phone number (from a different company), try to use that for verification. Most major phone carriers are supported.
Should you try different carriers and they all fail, please notify our support team with the name of the phone carriers you've tried. They can be contacted here.