In this study, a new method utilizing surface plasmon resonance (SPR) sensing technology based on the phase and angular interrogations for measuring the refractive index of a liquid prism is presented. An orthogonal sample box that combined the functions of a prism, cell box, and mirror is adopted to simplify the system and provide the convenience to implement the phase and angular interrogations. The angular interrogation is achieved by the motorized rotation stage with the new sample box, and the phase interrogation is achieved by the linear polarization interferometry between the s- and p-polarization components. The amplitude reflectivity and the phase angle, which are the functions of the incident angle, are obtained by the reflection intensity and the interference intensity of the lights directly. A sensitivity of $7.5\times {10}^7$ refractive index unit (RIU)/0.1° and a dynamic range of 0.5 RIU are obtained experimentally and theoretically.