Is there a way to add a field in this layout/display?
Only through API or by modifying the source. CBSubs for example does this using the onAfterBackendUsersList trigger. I'm not sure if CB Auto Actions can do this, but you can try with a Code action that's set to return the results of your PHP as "return". Your usage needs to return an array. Example usage as follows.
Code:
public function onAfterBackendUsersList( $listId, &$rows, &$pageNav, &$search, &$lists, $option, $select_tag_attribs ) {
$columns = array();
foreach ( $rows as $row ) {
$columns[$row->id] = $row->cb_company;
}
return array( CBPTXT::T( 'Company' ) => $columns );
}
Please see the below tutorial for further trigger usage information.
www.joomlapolis.com/support/tutorials/120-api-usage/18358-using-cb-triggers