Brillouin scattering measurements have been carried out for the first time on $K_{0.3}MoO_3$. The spectrum reveals two bulk modes at 18 and 27 GHz and a Rayleigh surface mode at 6 GHz. Both the bulk modes and the surface mode exhibit changes at the Peierls transition (180 K). Interestingly, the 18 GHz mode also shows softening at the incommensurate-commensurate transition around 100 K, suggesting the important role of phasons.