Phase Four stereo LPs go back to the early 1960s. I think that Decca was trying to improve stereo, but I don't think that the Phase Four refers to 4 channel. Here is a historical link:
http://www.gramophone.net/Issue/Page/February%201962/18/859905/DECCA+PHASE4+STEREO
http://www.gramophone.net/Issue/Page/February%201962/18/859905/DECCA+PHASE4+STEREO