The two high-temperature structures (identified as phase III and phase IV) of poly(p-hydroxybenzoic acid) (PHBA) are investigated through a molecular modeling methodology employing a Monte Carlo sampling of configurational phase space. Realistic chains of PHBA are represented by the explicit atom representation of the dimer repeat unit of the unit cell. States are sampled from the NVT ensemble using a scheme consisting of (1) valence angle and torsional angle variations and (2) rigid body rotations of the chain about the chain axis. Simulated X-ray diffraction data for the two phases are compared with experimental data from the literature. Intermolecular orientational probability density distributions indicate that phase III exhibits a wide range of intermolecular phenylene orientations, but with a retention of a herringbone-type packing in the a-b plane. The phenylene rings; of phase ni experience a greater intermolecular orientational freedom over phase III, but without free rotation. Intramolecular orientational probability density distributions indicate a preference for staggering the successive phenylene rings along the chain, with phase IV exhibiting a higher probability of the coplanar arrangement over that of phase III. The packing environments do not impose any severe restrictions on the torsion angles; the torsional angle populations of phases III and IV exhibited only minor variations relative to those exhibited by the individual chains free of interchain interactions.