Far-infrared reflectivity measurements in the frequency range 40-650 cm-1 at T=10, 100, 150 and 300K have been performed on degenerate n-type Cd3P2 samples. The experimental results are fitted with a model dielectric function. The authors use the Drude/linear oscillators equation for a coupled-plasmon-phonon system. The best fit of the theoretical curve to the experimental data is obtained using six independent transverse phonon modes with temperature-independent eigenfrequencies and oscillator strengths and temperature-dependent damping constants. For the static dielectric constant a temperature-independent value is found of 23+or-1.