As I have stated in your other three threads on this same project, the transformer is not critical. The frequencies used by the modem are the same as your DTMF. The impedance of a modem transformer is designed to be matched to the POTS line, the same as your DTMF receiver. The "primary", if you insist on distinguishing the (nearly identical) windings, is the side connected to the POTS line, the same as your DTMF decoder.
The circuit that you show part of, would pass DC through the windings. This should be avoided. The best thing for you to do is to trace the very simple circuit on that modem and copy it. After you have traced the circuit, please draw it and we can confirm it for you.
PLEASE DO NOT START ANOTHER THREAD FOR THIS PROJECT. USE ONE OF THE FOUR YOU HAVE ALREADY WRITTEN.