There are three basic modulation effects used in guitar pedals today : phase shift , chorus, and flanger. The most simple difference between them is that both a chorus and flange effect come from a modulated delay that’s mixed back into the original signal, but a phaser uses no delay at all. 

The phase shift gives that sci sound 60's swirling sound. One guitarist of note that used phase shifting, Eddie Van Halen

The chorus effect is created by doubling your guitar signal and slightly shifting the second one out of time and pitch with the original

The main differences between a flanger and a chorus is that the flanger uses a shorter delay. 

• Chorus effects (3)
• Flanger Effect (0)
• Phase Shift Effect (1)
• Tremolo (1)