  Phase diffusion represents a crucial obstacle towards the implementation of
high precision interferometric measurements and phase shift based communication
channels. Here we present a nearly optimal interferometric scheme based on
homodyne detection and coherent signals for the detection of a phase shift in
the presence of large phase diffusion. In our scheme the ultimate bound to
interferometric sensitivity is achieved already for a small number of
measurements, of the order of hundreds, without using nonclassical light.
