Optical properties of n-doped (Si) hexagonal Ga1-xMnxN films (x=0.015) grown by metal-organic chemical-vapor deposition (MOCVD) on c-plane sapphire substrates have been studied by infrared reflectance spectroscopy. The effect of free carriers on GaMnN optical phonons, namely E1(LO) and E1(TO), is explored. It is found that the frequency of E1(LO) increases with increasing free carrier concentration. The absorption coefficient (α) is calculated for the 200-2000 cm-1 range and the maximum value of α is found to be ∼105 cm-1 at a frequency of 560 cm-1. With increasing free carrier concentration, the FWHM of the absorption peak increased by 35%-40% as compared to an unintentionally doped (≪1×1016 cm-3) film.