A monolithically integrated InP/InGaAsP 1?5 optical phased-array switch is demonstrated for broadband wavelength-division multiplexed (WDM) optical packet switching (OPS) application. Using the wide optical bandwidth of the switch, we achieve error-free forwarding of 320-Gbps (40-Gbps?8 channel) WDM signal with less than 1.3-dB penalty. Since the switch consists of only phase-modulating section, it is free from nonlinear signal distortion and inter-channel crosstalks, allowing large dynamic range of input power. The application to WDM-OPS testbed is demonstrated successfully, where 320-Gbps WDM payloads are routed synchronously to the optical label.