migmag-1.0.x-dev/tests/modules/migmag_missing_plugins/migmag_missing_plugins.module

<?php

/**
 * @file
 * Contains hooks implemented by migmag_missing_plugins.
 */

/**
 * Implements hook_migrate_field_info_alter().
 */
function migmag_missing_plugins_migrate_field_info_alter(&$definitions) {
  unset($definitions['phone']);
}