The first-order orthorhombic-rhombohedral phase transition of La1-x Sr (x) Ga1-y Mn (y) O-3 (LSGMn) crystals is studied by Raman spectroscopy. An increase in Mn content causes significant changes in Raman spectra, especially in the high-wavenumber spectral range. The Raman spectrum of La1-x Sr (x) Ga1-y Mn (y) O-3 compound with x = y = 0.02 is dominated by MnO6 internal vibrations. Moreover, a change in the spectrum of this crystal is observed when the 785-nm excitation line is used. Essential reduction in the number of Raman modes during the phase transition is experimentally observed. The temperature of the phase transition decreases with increasing Sr and Mn contents, at the rate of about 20 K/at%.