"unable to setup LINE Port to make it work." is not much help in determining what problem you are having.
With the default settings for the 312's LINE port, when a door button is pressed and the Valcom rings the LINE port of the OBi312 the LINE LED of the OBi should flash and an analogue phone plugged into the OBi's PHONE jack should ring. Taking that phone off-hook should answer the call and two-way conversation with the door plate should ensue. Does all that happen?
I assume that instead of the analogue phone in the OBi's PHONE jack you instead want to "remote" that using SIP Is that correct?
With the analogue phone still in the OBi's PHONE jack is the SIP configuration such that dialling the requisite number on the analogue phone rings the target SIP phone and, when it answers the call, bothway conversation is possible?
If all good so far then change the LINE port InboundCallRoute from its default
ph
to the appropriate customisation of
spx(nnnn)
where x is the number 1 through 4 of the SP configured for the SIP provider and nnnn is the number of the SIP phone. (May be more or less than 4 digits.)