We have proposed an 8 phase-shift-keying (PSK) optical millimeter-wave (MMW) signal generation scheme with frequency quintupling enabled by an electro-optical phase modulator (PM) and a wavelength selective switch. In this scheme, the radio frequency (RF) carrier with 8PSK signal is modulated on the lightwave via the PM with simple precoding but constant Euclidean distance, and is recovered to the original 8PSK signal with the frequency-quintupling RF carrier based on the phase periodicity of an 8PSK signal. By optimizing the voltage amplitude of the 8PSK RF driving signal, the generated frequency-quintupled 8PSK MMW signal is maximized at a given laser launch power. A radio over fiber simulation link is built to demonstrate the theoretical analysis. The simulated constellations and bit-error-rate curves show that the frequency-quintupling 8PSK MMW signal has good transmission performance. The simulation results agree well with our theoretical prediction.