We report the first measurements of FIR and MIR reflectivity of single-crystal monoclinic antiferromagnetic copper monoxide (CuO) in a wide temperature range (7-300 K) when b-axis and ac-plane polarized modes are completely separated and excited in transverse geometry. Previously reported softening of the A u3 mode at the Néel transition is confirmed and found to be up to two times more significant (about 10%). For the first time an emergence of several new IR-active lines at low temperatures is observed. The highest frequency new mode at 690 cm-1 strongly hardens and strengthens with cooling. The data are discussed in terms of strong spin-phonon coupling and possible charge disproportionation at low T.