Using a phenomenological lattice model incorporating the long-range Coulomb and charge transfer caused by the deformation of the electron shells of the overlapping ions and the Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbor ions and the van der Waals (vdW) interaction, we present a comprehensive study to understand the effects of pressure on the elastic behavior as ductility (brittleness) and thermodynamical properties of Ga1-xInxP. Estimated phase-transition pressure and the vast volume discontinuity in pressure-volume phase diagram confirm the structural phase transition from zinc blende (B3) to rock salt (B1) phase. From the elastic constants the Poisson's ratio v, the ratio R-S/B of S (Voigt averaged shear modulus) over B (bulk modulus), elastic wave velocity, average wave velocity and thermodynamical property Debye temperature is calculated. The Poisson's ratio v and the ratio R-S/B allows one to conclude that Ga1-xInxP is brittle in zinc blende (B3) and ductile nature is inferred in sodium chloride (B1) phase. To our knowledge this is the first quantitative theoretical prediction of the doping and pressure dependent elastic properties for mixed valent Ga1-xInxP compounds and still awaits experimental confirmations. (C) 2010 Elsevier Ltd. All rights reserved.