$element['numbers'] = array(
    '#type' => 'textfield',
    '#title' => $element['#title'],
    '#default_value' => $element['#default_value'],
    '#description' => $element['#description'],
  );
  return $element;

foreach($a as $b) {
  $element['asdf'][] = array(
    '#type' => 'phone_numbers',
    '#title' => $b,
    '#default_value' => $element['#default_value'],
    '#description' => $element['#description'],
  );
}