High-dispersion high signal-to-noise ratio spectrograms of Phi Per have been obtained. The radial velocities of various spectral features have been measured and an orbit solution obtained. The Phi Persei system is found to consist of a 21 solar mass star, whose V sin i is 450 km/s, and a 3.4 solar mass secondary. The secondary is peculiar in that He II 4686 A emission arises from within its vicinity. It is suggested that the secondary is the helium core of a once more massive star, its mass having been transferred to the primary. Both stars in the system have circumstellar disks and the dimensions of these disks are discussed.