From what you described, I think OBi110 can actually detect the ringing from intercom, but might not have enough time to ring the phone. We may try to modify some settings --
1) Shorten LINE port ring delay, go to:
Physical Interface -> LINE port -> RingDelay -> 0 (default is 4 seconds, which might be too long)
2) Shorten Ring validation time, go to:
Physical Interface -> LINE port -> RingValidationTime -> 150 ms
3) Shorten Ring Indication delay time, go to:
Physical Interface -> LINE port -> RingIndicationDelayTime -> 256 ms
Give it a try, see if you can hear the ringing on the phone ..