John was pretty much to the point and right on, but since I never know when to shut up, here's some more technical stuff...
flangers have a more of a rotation or sweeping effect than phase shifters, a little like an old leslie. Like John said, it can be used to create the jet sound. Phasers modulate less but produce a similar effect. the old hendrix uni-vibe is really the 1st phase shifter and created a modulating effect. Check out his Star Spangled Banner in the movie Woodstock. You might be struggling with the difference because they are so related as to be nearly the same.
both create a "wet" sound by shifting a portion of the signal a little out of phase with the rest (Phaser or Phase shifter). The idea is to use a delay circuit (usually an RC) to move parts of the main signal sine wave out of phase with the original. The length of the delay and filter adjustment will determine how often and how much of the signal will cross and cancel, or sync and reinforce. This is usually applied in a series of stages to create the sweep sound.
flangers create more delay points than phase shifters and can be a smoother effect at smaller delay rates because the signal can acquire more harmonic frequencies. However many flanger devices will allow the user to greatly vary the delay times creating a greater rotating or sweeping effect which can become a little overdone. The slowest sweep and largest amplitude creates the jet sound.
The sound can get annoying as John mentioned. Frampton uses one on just about the entire live album which makes his guitar kinda muddy, but tends to smooth the tone to get to that "I just ate 2 qualudes" effect.
I used an EH Smallstone in the 70's and tried to graduate to a flanger in the 80's, but hated it and sold the flanger to a keys player and still have the smallstone.
highly technical brief if you want to build one.
http://www.geofex.com/Article_Folders/p … phase.html
That's alright, I got my guitar
-Jimi Hendrix
