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Phonon modes in MOVPE grown In0.5Ga0.5P containing domains with CuPt-type ordering in the cationic sublattice along the [-111] and [1-11] directions were studied by means of FIR and Raman spectroscopy. The observed polarization dependence of the transmittance of the FIR radiation near 370 cm-1 suggests that this TO-type mode is characteristic not only of the disordered alloy, but also of the ordered InGaP2. Ordering-related features observed by Raman spectroscopy include the extra (354 cm-1) phonon mode appearing (although not clearly resolved) in the allowed z(xy)z  scattering, and a clear difference between the spectra taken in z(x'x')z and z(y'y')z configurations. All these effects are noticeably smaller for the InGaP films with lower degree of ordering due to doping with Bi during its growth.