Chorus, tremolo, phase and flange are all referred to as modulation effects. They add depth, dimension and movement to a guitar's natural sound without distorting it, but they all have their own unique characteristics.
Common to most pedals is a rate control that adjusts the speed of the effect and a depth control that adjusts the intensity of the effect.
Chorus is a stunning shimmer effect that adds width to your tone. You'll have heard it used by artists as diverse as Prince, The Police and Nirvana.
Tremolo is the effect of a guitar sound's volume cutting in and out at a variety of speeds. If you've heard the song How Soon Is Now by The Smiths you'll know how it sounds.
Phase splits the signal in two, moves one of those paths out of phase then blends it back in with the original, so the motion of that in phase/out of phase relationship can be heard. That might sound technical but you will have heard this effect all over the late 90s recordings of Radiohead, Incubus and even Eruption by Van Halen.
Flange works in a similar way to phase, but takes it to even greater extremes. You will have heard it on songs like Are You Gonna Go My Way by Lenny Kravitz or Nobody's Fault But Mine by Led Zeppelin.