In this paper the dynamics of a trapped two-level atom interacting with a beam of electromagnetic wave of circular polarization is studied. In a frame rotating with the atomic transition frequency ω0, the motion of the atom is governed by a nonlinear coupled Jaynes-Cummings (JC) Hamiltonian. By means of this nonlinear Hamiltonian, we study the atomic inversion, squeezing effect of the vibration mode and that of the atomic dipole, and the phase property as well as its fluctuation of the vibration mode. In the Lamb-Dicke limit, we get the results similar to those of the JC model; beyond the Lamb-Dicke limit, we find the evolution of these quantities becomes very complicated. The nonlinearity weakens the collapse-revival phenomenon of the atomic inversion and the squeezing effect; the evolution of the cosine phase operator becomes less predetermined with its fluctuation not enlarged.