We propose a phase optimization technique for sidelobe suppression in OFDM system. The technique is based on idea that phase shift to some of the transmit symbols within the symbol constellation plane can lead to significant sidelobe suppression. The sidelobes are reduced by optimizing using iterative method the phases of some subcarriers on the left and right hand side of the used OFDM spectrum. The proposed technique requires a small amount of side information that needs to be transmitted. Simulation results show that the proposed technique can reduce the sidelobes by significant amount.