Hi
Here solution for WINDOWS objectsid:
// LIB .............................
class LDAP_OBJECT_SID {
    
    public function toString($SID_BINARY) {
        
        $split = str_split($SID_BINARY, 8);
        $hexArray = array();
        foreach ($split as $key => $byte) { 
           $hexArray[$key] = strToUpper(substr('0'.dechex(bindec($byte)), -2));  
        }
        
        $BLOCK_COUNT = hexdec($hexArray[1]);
        $DEC_GROUP['SUB-ID-BLOCKS'] = array();
        for ($i=0; $i<$BLOCK_COUNT; $i++) {
            $offset = 8 + (4 * $i);
            $DEC_GROUP['SUB-ID-BLOCKS'][$i] = array();
            $DEC_GROUP['SUB-ID-BLOCKS'][$i][1] = hexdec($hexArray[$offset+3]);
            $DEC_GROUP['SUB-ID-BLOCKS'][$i][2] = hexdec($hexArray[$offset+2]);
            $DEC_GROUP['SUB-ID-BLOCKS'][$i][3] = hexdec($hexArray[$offset+1]);
            $DEC_GROUP['SUB-ID-BLOCKS'][$i][4] = hexdec($hexArray[$offset]);
            
        }
        $SID = 'S-'.hexdec($hexArray[0]).'-'.$this->byte6ToLong(
            hexdec($hexArray[2]), 
            hexdec($hexArray[3]), 
            hexdec($hexArray[4]), 
            hexdec($hexArray[5]), 
            hexdec($hexArray[6]), 
            hexdec($hexArray[7])
        );
        foreach ($DEC_GROUP['SUB-ID-BLOCKS'] as $BLOCK) {
            $SID .= '-'.$this->byte4ToLong(
                $BLOCK[1], 
                $BLOCK[2], 
                $BLOCK[3], 
                $BLOCK[4]
            );
        }
        return $SID;
        
    }
    
    private function byte6ToLong($b1, $b2, $b3, $b4, $b5, $b6) {
        $byte6ToLong = $b1;
        $byte6ToLong = $byte6ToLong*256 + $b2;
        $byte6ToLong = $byte6ToLong*256 + $b3;
        $byte6ToLong = $byte6ToLong*256 + $b4;
        $byte6ToLong = $byte6ToLong*256 + $b5;
        $byte6ToLong = $byte6ToLong*256 + $b6;
        return $byte6ToLong;
    }  
    
    private function byte4ToLong($b1, $b2, $b3, $b4) {
        $byte4ToLong = $b1;
        $byte4ToLong = $byte4ToLong*256 + $b2;
        $byte4ToLong = $byte4ToLong*256 + $b3;
        $byte4ToLong = $byte4ToLong*256 + $b4;
        return $byte4ToLong;
    }   

}

TEST:

$sr=ldap_search($conn, $base_dn, $filter,$fields);
$entry = ldap_first_entry($conn, $sr);
$objectsid_binary = ldap_get_values_len($conn, $entry, "objectsid");

$Obj = new LDAP_OBJECT_SID();
echo $Obj->toString($objectsid_binary[0]);