Crystals of bismuth fluoride BiF3 grown from a melt were studied for the first time by optical spectroscopy methods and calculated from first principles in the phonon excitations region. A study of IR reflectance spectra in polarized light was carried out. The parameters of optical phonons were obtained. In the IR reflectance spectra, a low-frequency rise in the range <500 cm-1, characteristic of conductive materials, is observed. The reflection spectra were analyzed within the framework of the Drude-Lorentz model, taking into account the contribution of ionic conductivity. An ab initio calculation of the phonon spectrum of a BiF3 crystal was carried out and the relationship between theoretical and experimental data was analyzed.