title: How to add custom fields to comments form in WordPress/WooCommerce 3+
body: <p><a href="https://i.stack.imgur.com/OjFhN.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/OjFhN.jpg" alt="Example"></a></p>
  
  <p>I'm trying to add a "Phone" field in the product comments (WooComerce 3+).
  *For unregistered users too (guests). 
  Phone number should only be seen by the administrator in the admin panel. </p>
  
  <p>*Phone field need make "<strong>Required</strong>".</p>
  
  <p>I tried this code, but this not work:</p>
  
  <pre><code>function true_phone_number_field( $fields ) {
  $fields['phone'] = '&lt;p class="comment-form-phone"&gt;&lt;label for="phone"&gt;Phone&lt;/label&gt; &lt;input id="phone" name="phone" type="text" value="" size="30" /&gt;&lt;/p&gt;';
  }
  add_filter( 'comment_form_default_fields', 'true_phone_number_field');
  </code></pre>