A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance (SPR) sensing system with ultra-high resolution performance is presented. The system exhibits a root-mean-square phase fluctuation of +-0.0028 angle over a period of 45 min, i.e. a resolution of +-5.2*10^(-9) refractive index units. The enhanced performance has been achieved through the incorporation of three design elements: a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected, a differential measurement scheme to eliminate spurious signals not related to the sensor response, and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulator. Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.