We use time- and angle-resolved photoemission spectroscopy in the extreme ultraviolet to measure the time- and momentum-dependent electronic structures of photoexcited K_0.3MoO₃. Prompt depletion of the charge-density wave condensate launches coherent oscillations of the amplitude mode, observed as a 1.7-THz-frequency modulation of the bonding band position. In contrast, the antibonding band oscillates at about half this frequency. We attribute these oscillations to coherent excitation of phasons via parametric amplification of phase fluctuations.