The potential energy surface (PES) of n-p-phenyls, with n from 2 to 5, has been obtained from ab initio calculations relevant to a few fragments into which the molecule can be decomposed. These PES have been fitted with a single Gay-Berne model that has been used in Monte Carlo NPT and Gibbs ensemble simulations. The results we obtain are in fairly, good agreement with experiment in the case of biphenyl, while only a low density fluid phase (gas) is obtained for p-terphenyl and longer molecules.