We report the formation of a reverse micellar cubic mesophase of symmetry Fm (3) over barm (Q(225)) in ternary mixtures of soy bean phosphatidylcholine (PC), water, and an organic solvent, including cyclohexane, (R)-(+)-limonene, and isooctane, studied by small-angle X-ray scattering (SAXS) and oscillatory shear rheology at room temperature. The mesophase structure consists of a compact packing of remarkably large reverse micelles in a face-centered cubic (fcc) lattice, a type of micellar packing not yet reported for reverse micellar mesophases. Form factor fitting in the pure L-2 phase and in the Fm (3) over barm-L-2 coexistence region yields quantitative estimations of the PC interface rigidity. The compact Fm (3) over barm structure results mainly from release of lipid tail frustration and hard-sphere interactions between monodisperse micelles, as suggested by a comparison with the Fd (3) over barm structure found in the PC/water/alpha-tocopherol system.