How do I get dropdown selected value?

I need to get the selected dropdown value (index would be helpful, too) to use in this function:

add_action('wpcf7_before_send_mail', 'do_stuff_with_data');
function do_stuff_with_data($formdata) {
   if ($formdata->id() == 1000) {
      $submission = WPCF7_Submission::get_instance();
      if ($submission) {
         $posted_data = $submission->get_posted_data();
      }
      $item1 = $posted_data['text_field'];
      $item2 = $posted_data['dropdown'];
   }
}

That gets text field value, but does not get dropdown selection value.

I’d rather keep this PHP and avoid escaping JS/jQuery to do a selectedIndex on the DOM (I presume the “id” option in the CF7 tag would be what I’d use).