[praash]

Phase shifts make no practical difference when you're equalizing headphones. You really shouldn't need to use notch filters there.

EQ phase is relevant if the dry signal has a chance to mix with the EQ output.

Changes in phase is not "distortion". When you end up making large boosts (especially to make sub bass audible), that's when your headphone drivers might start to distort sound. This is fixed with less volume, obviously.

[serverholic]

An EQ that cuts frequencies can actually increase the amplitude of the waveform due to phase shifts. It's not just boosting. What I'm talking about is more relevant on analog gear which is more sensitive to volume.