Non-linear Dynamics of an Informational Vacuum: Phase Saturation as the Origin of Galactic Acceleration

We present a scalar-field framework in which spacetime is treated as an informational substrate with finite phase capacity. A logarithmic potential naturally induces a non-linear equation of motion whose saturation regime reproduces flat galactic rotation curves without invoking dark matter. The theory introduces no galaxy-dependent free parameters and predicts a universal low-acceleration scale emerging from cosmological constants.