Reflection anisotropy spectroscopy (RAS) and reflection high-energy electron diffraction (RHEED) were applied to study clean InP(001) surfaces prepared by molecular beam epitaxy (MBE). At phosphorus beam equivalent pressures (BEPs) between 3.5x10(-7) and 3.5x10(-6) mbar and substrate temperature (T-S) falling from 590 to 150 degrees C, (2x4), (2x1), (2x2), and c(4x4) RHEED patterns are observed. The main RAS features, observed at 1.7-1.9 and 2.6-2.9 eV are assigned to In and P dimers, respectively. The above reconstruction sequence is associated closely with transformations identified in RAS signatures that are induced by progressively increasing the P surface coverage. The RAS results also imply the existence of (2x4)alpha and (2x4)beta phases. A surface-phase diagram for MBE-grown (001) InP, in the whole range of T-S and phosphorus BEPs is proposed. (C) 1997 American Institute of Physics.