We show that only one of the four Raman active modes in Ga0.47In0.53As shows the required symmetry behavior for longitudinal optical (LO) phonons. An additional mode previously supposed to be LO shows mixed‐mode behavior and may be disorder activated. Our results prove that only one phonon mode in Ga0.47In0.53As is active in scattering electronic carriers, and thus in determining both electron and hole mobilities.