Hi:
Plug the phone directly into the OBi for testing purposes. Does it work properly? If so, then you definitely have a wiring fault. Some examples: somebody drove a cable staple through the jacket and shorted two wires, a rodent chewed on it, or one of the Cat 5 modular blocks is incorrectly wired, or there is some other device connected to the phone wiring that is causing the problem.
If you have a multimeter and a spare phone cord, then cut one end off of the phone cord, strip the wires, and plug the other end into one of the wall jacks. There should be infinite resistance between all of the wires.