get_entries
Use the get_entries to retrieve the entries for a form. Make sure that you set the page_size option, or else it will return only 20 results.
$search_criteria['field_filters'][] = array('key' => '6', 'operator' => 'in', 'value' => array('1')); // 1 = not approved, 2 = approved but not send, 3 = approved and sent
$search_criteria['status'] = 'active';
$paging = array( 'offset' => 0, 'page_size' => 200 );
$entries = GFAPI::get_entries(2, $search_criteria, null, $paging);