Cell phone audio traditionally only covered 300Hz-3.4kHz before being lossily compressed down to 4kbps (or sometimes higher, depending on network, load in that service area, etc). That is complete shit. Recently, there have been other protocols adopted with greater bandwidth (all the way up to 7kHz, which is still several khz short of covering all the content of speech, but considerably less terrible) and less compression, but if you have audio that's actually good and not merely passable, it's probably because your phone is actually transmitting audio as voip, with a much better codec then is used for cellphone audio transmitted over the standard channel.