Lanthanum gallate (LaGaO₃) is known to undergo orthorhombic to rhombohedral first order phase transition at 150 °C. In this article we have shown that by introducing 2% La deficiency in the system, coexistence of above two phases can be obtained at lower temperature and a complete phase transition occurs at 200 °C. The evolution of structural parameters of the system with temperature is reported from X-ray diffraction measurements and Rietveld analysis of the diffraction patterns. The change in local octahedral distortion due to 2% La deficiency is revealed through the shift in the phonon modes of GaO₆ octahedra, in both orthorhombic and rhombohedral phase.