Yes, but choccy biscuits and tea/coffee can induce absent mindness in OpenReach engineers.
If the incoming pair are connected and the socket is a master with the ring capacitor and the phone plugged into that socket is a known working phone then it has to be an exchange fault.
One type of exchange has been known to lose the ringing voltage supply to a card ( PCB ) carrying several SLICs ( Subscriber Line Interface Circuit ) meaning these subs have the fault you appear to have. I was told the loss of ringing voltage was not detected until the subs affected reported DNR ( Disputed No Ringing ).
