
But what are they and how do they work? Let's take a look...
What is a Phaser?
To understand what a Phaser is, it's probably a good idea to understand what phase is in the first place! Phase refers to a point on a cycle of a waveform, measured in degrees. Don't get put off just yet, it'll become clear as I explain about what a Phaser is.
A Phaser is an effects unit that splits the signal into two paths, delays one of the paths very slightly, then mixes them back together. It doesn't do this across all frequency bands equally - a high frequency might be delayed more than a lower frequency, depending on the sound.
The effect caused when the delayed sound cancels certain parts of the source sound out due to being slightly "out of phase" with it creates an otherworldly effect.
This is typically modulated with an LFO (Low frequency oscillator) in order to make it move consistently and give a sweeping kind of effect.
Another cool thing to note - when the two signals on a constant wave are 180 degrees out of phase, you hear no sound whatsoever.

Now, a Flanger is a specific type of Phaser. Whereas the Phaser delays things differently depending on the frequency, a Flanger is all for equal rights and delays all frequencies equally. This makes a more harmonic and - dare I say it - natural sound.
What does a Phaser / Flanger contain?
Rate - This is the speed at which the LFO modulates the delay time of the slightly out of phase signal.
Depth - This is the intensity of the effect
Mode / Type - Some Phasers / Flangers have different algorithms they use to calculate how to produce the effect. This allows you to switch between them.
Feedback / Resonance - Defines how much of the effect signal is fed back to the input - this can make some crazy resonant sounds.
Wet/Dry - This controls what percentage of the output from the unit has the effect applied and what percentage is the original source sound.
Some useful techniques
1. Jet Plane!

2. Subtle funky wah
Add a little bit of phase with a decent amount of depth to a clean, compressed guitar signal and voila! Instant space-funk!
3. Lush Synth Pads
Add some phase to your pads, heavy on the depth and a little bit of resonance (if you have it) to get a nice high pitched overtone and they'll be lusher than ever before!