Distortion has its place in music, but unwanted distortion can ruin a recording. Distortion can result from a microphone receiving too much sound. Think of someone on the other end of the phone screaming; their voice will be far from clear. Some simple solutions include moving the mic farther from the source, or even using a different type of microphone.
You can read more tips about distortion here: http://www.prosoundweb.com/article/church_sound_audio_distortion_–_finding_the_source_and_clearing_the_air/