The properties of the phase evolution in the system of a single-mode field interacting with a two-level atom via multiphoton process in a high Q cavity filled with the Kerr-like medium are studied by means of the non-relativistic quantum electrodynamics. The influences of coupling constant X, frequency detuning △ and transfering number k on the phase probability distribution, the phase diffusion and the frequency shift are emphatically discussed under the strong field condition.