TelephoneField.php

<?php

namespace Drupal\telephone\Plugin\migrate\field\d7;

use Drupal\migrate_drupal\Plugin\migrate\field\FieldPluginBase;

/**
 * @MigrateField(
 *   id = "telephone",
 *   core = {7},
 *   source_module = "telephone",
 *   destination_module = "telephone"
 * )
 */
class TelephoneField extends FieldPluginBase {
  
  /**
   * {@inheritdoc}
   */
  public function getFieldWidgetMap() {
    // The widget IDs are identical in Drupal 7 and 8, so we do not need any
    // mapping.
    return [];
  }
  
  /**
   * {@inheritdoc}
   */
  public function getFieldFormatterMap() {
    return [
      'text_plain' => 'string',
      'telephone_link' => 'telephone_link',
    ];
  }

}