This object references, by entPhysicalIndex value, the physical port entity in the IP Office's entity MIB that this phone is connected to; it is set to 0 if no specific physical port mapping applies, such as for an IP phone not tied to a physical port on the IP Office itself. Administrators use it to trace a phone entry back to its exact physical connection point on the chassis when that mapping exists. For example, a digital phone plugged directly into the control unit would show a nonzero value here pointing to its specific physical port entity, while a remote IP phone connecting over the LAN would show 0.