A system and method for managing phases in a multiphase switching power supply turns off a phase in light load conditions and turns on a phase in heavier load conditions. The increase or decrease in the number of phases changes the efficiency of the power supply in response to operating conditions. The phases of the power supply may be synchronized and interleaved. Input current or power representing power supply loading provides a criteria for switching phases on or off. The input current can be taken from an input current sense resistor. The input power can be determined based on a control for managing phases. Turning a phase off causes remaining phases to have an increased on-time or gain to smooth the transition between differing numbers of active phases.