Spoof surface plasmon polaritons (SSPPs) have aroused widespread concern due to their strong ability in field confinement at low frequencies. For miniaturized integrated circuits, there is a pressing need for nonreciprocal spoof plasmonic platforms that provide diode functionalities. In this letter, we report the realization of nonreciprocal phase shifting in SSPPs using the transverse Faraday effect. A plasmonic coupled line is constructed by flipped stacking two corrugated metallic strips, in order to enhance the mode coupling between evanescent waves that carry opposite transverse spin angular momenta. With a transverse magnetized ferrite cladding, the SSPP mode is split into two circularly-polarized ones that show different propagation constants over a broad band. A nonreciprocal phase shifter compatible to standard microstrips is designed to validate the breaking of time-reversal symmetry in SSPPs. Microwave measurement demonstrates a differential phase shift up to 46.2°/cm from 12 GHz to 15 GHz. Owing to the advantages of strong field confinement and contactless ferrite integration, the proposed method enables an alternative pathway for nonreciprocal spoof interconnects.