Include Phone number field

This will most probably never be accepted as this is a custom field that is not part of Drupal Core (especially with custom field being added through the UI). You should instead create a new custom module or modify an existing one that would implement the API hook and include the required field. There is no real reason to modify the original module.

We are not asking to modify the module, just an example of how to use hook_bulk_user_registration_extra_fields() or how to add a custom field.