Phaser is to the 70's what Chorus is to the 80's, such a great movement within your tone with the additional benefit of adding groove to the overall song. Back in the 70's the phaser to rule them all was the MXR Phase 90 due to use by EVH, however the popularity of that pedal encouraged companies such as BOSS & Electro-Harmonix to create their own versions.
Using the single knob model the Phase 90 & 45 laid the ground for, EHX added an interesting "color" switch allowing players to switch between a much more subtle and a more obvious tonal change effectively giving the equivalent of two pedals in one.
This is the V2 model, you'll likely notice how the speed ramps up much faster than on the V1 version we have on TonePedia. The V2 is also overall a little more transparent which lets through more of the dry tone.