The most common dimmer type in entertainment lighting systems. Uses a thyristor (SCR or Triac) to switch the AC waveform to vary the amount of power to a load. Produces a non-sinusoidal voltage output waveform, and draws current in a non-sinusoidal waveform that produces harmonics.
Derek is No. 3 meant to be IGBT ( Insulated Gate Bipolar Transistor).
From my electronic studies I believe you will find a number IGBT Dimmers are in the phase control family. Actually they are known as reverse phase control.
Because instead of turning on part way through the AC phase cycle IGBT's can turn off part way through the AC phase cycle controlling the power to the load. There is less of a spike raised at the turn off of the AC cycle part way through then there is using SCR's, TRIAC'S that turn on part way throught the AC cycle. So interference is less.
If you are referring to IGBT's being used in PWM (Pulse width Modulation) dimmers which produce Sine waves then this would be a non phase control system.