Auto-fill Custom comment fields

You can store these values in cookies and fill them when you are creating form inputs.

So in save_comment_meta_data add something like this:

$commenter_data = array(
  'phone' => $phone,
  ...
);
setcookie('commenter_data', serialize($commenter_data), time()+1209600, COOKIEPATH, COOKIE_DOMAIN, false);

And then when you’re creating form:

$commenter_data = isset($_COOKIE['commenter_data']) ? unserialize($_COOKIE['commenter_data]) : array();
echo '<p class="comment-form-title">'.
'<label for="phone">' . __( 'Commenter Phone' ) . '</label>'.
'<input id="phone" name="phone" type="text" size="30"  tabindex="5" value="'. (array_key_exists('phone', $commenter_data) ? $commenter_data['phone'] : '') .'" /></p>';