I look at it this way,.....
Phaser sounds like a non-watery flanger, there's still a bit of a whoosh, but none of that metallic "water against metal siding" noise effect the Flanger has, the color I'd describe to the sound would be gray or white
A flanger can be anything from that aforementioned sound to something like a Jet Plane, it's very watery, and is the #1 effect used for hokey alien effects in movies from the 80's (and multi-effects unit demo patches for that matter). I describe the color of the sound sort of a dark teal or purple depending upon the sound. The name comes from an old studio trick where one had 2 tape reels with identical recordings on them, and the engineer in the studio would put his finger on one of the recorder's reels to put them slightly out-of-phase (time) with each other.....the tequnique was called "Flanging" hence the name flanger and produced the same sound.
Chorus is a close relative of flanger as they both work using time delays instead of phase (which is why a Phaser is called a phaser, it twists the phase of the signal whereas a flanger and chorus are basically a delay pedal set really low). Chorus is done by making copies of the signal and modulating them slightly to put them ever-so lightly out of tune with each other. Same principle as the FLanger just closer tolerances, and the name Chorus implies that it's supposed to sound more like a "chorus" of whatever is run through the effect.
The above is also why the EHX PolyChorus has delay settings on it, it's basically a really fancy schmancy delay that can do chorus, flange, and double tracking.
