Magnetophonon resonances were observed for the first time in single cr
ystals of black phosphorus in the temperature range from 77 to 200 K u
sing pulsed high magnetic fields up to 40 T. Five maxima in the magnet
oresistance were observed for the field parallel to the a-axis. From t
hese magneto-oscillations the longitudinal optical phonon B(lu) and B(
lg) modes are identified and their coupling is discussed.