The geometric and dynamic phases are generally treated as independent and together give rise to the total phase of a system. Here, we present a scenario in which these two phases become strongly interdependent. We achieve this by introducing a modified Young’s double-slit configuration that supports surface plasmon polaritons (SPPs) propagating between the slits. Remarkably, by varying the slit separation distance, and hence the dynamic SPP phase, by just a single plasmon wavelength, the geometric phase can be significantly modified.