To expand on the other comment. You wouldn't be able to tell the difference in a single sine wave with phase set to either 0 or 180 degrees. But if you add in another sine wave at 0 degrees, the two 0's will add up and the 0 and 180 will completely cancel.

Phase makes a huuuuge difference in audio engineering. There isn't a single song that gets mixed without intense consideration of phase interactions between the different tracks. Getting it wrong can result in catastrophic damage to the audio signal that reaches your ears. If you have a speaker capable, try switching the leads that feed the signal on one of the speakers and see how it sounds! Everything that's exactly the same between the two speakers will sound hollow and tinny, the frequency balance will completely degrade