I can hardly ever recommend "phase cancellation" on purpose. What is it you are trying to actually accomplish. You realize phase cancellation, true phase cancellation equals zero output. So you can actually simulate it by turning the volume slider all the way down.

When a wave is 180 degrees out of phase with a duplicate of itself, the result is silence. There is acoustic phase cancellation and electrical phase cancellation, but the principals and results are very much the same.

A TRS (tip-ring-sleeve) cable is a good example of (electrical) phase cancellation at work... The longer you make a signal cable (guitar cable) the better antennae it becomes, the typical guitar cable is unbalanced (just two wires). A balanced cable has three wires: a hot, a cold and a ground... Noise gets equally into both the hot and cold but is completely cancelled at the cable end by phase cancellation.

I also can never recommend plugging the output of something back to its input, this sets up another "things to avoid" situation in audio, called feedback.

So again, what are you trying to accomplish... Really? Let us know. Perhaps you want Phase shifting which degrades the sound, but gives use a useable effect if used with taste. Your ear/brain will immediately detect differences in phase, we use it as a highly developed skill to locate sounds. Your right ear and left ear often pickup the same sound, sound travels at 770 mph, but the very slightest difference in the time a sound arrives at one ear versus the other is detectable and allows you to know a lot about what it is and where it is.

Let us know.