Indicates on which phase or phases the given circuit is wired. For single phase devices, this object will always return phase1(1). For 3-phase devices with outlets wired to a single phase, this object will return phase1(1), phase2(2) or phase3(3). For 3-phase devices with outlets wired to two phases, this object will return phase1-2(4) for phases 1 and 2, phase2-3(5) for phases 2 and 3, and phase3-1(6) for phases 3 and 1. Devices that do not report phase connections will return unknown(0).