I'm known for using a ton of effects, and I use things like Phasers and Flangers for quick bursts of sound.
For example, I will have a phaser set to slow and deep sounding, and for a crescendo in a song, I will step on it for the last measure of a section, building into the next. I use it like a drummer would use a drum fill.
By the same token, I'll set a phaser for very fast and exreme, like a machine gun, and use it in a similar fashion.
It kind of drives me nuts to hear the periodic swirl of a phaser or flanger whooshing on and on in a song. I either want it to sound random or I want it to be subtle.
As a producer, I try to talk guitar players out of using a phaser or flanger for an entire song if it is sounding like "hey, I just bought a new pedal. Wanna hear it?" Use it for a couple of sections for dynamic changes.
Roger