A theoretical and numerical analysis of the transmission of phase_modulated laser pulses through a thin film with excitonic nonlinearity is performed. It is shown that, by choosing the modulation law, one can efficiently control the optical nonlinearity of the film down to the inversion of the sign of nonlinearity. Unique optical properties of thin semiconductor films attract considerable interest from the viewpoint of prospects for their practical applications. We have investigated the nonlinear transmission of a phasemodulated (chirped) ultrashort resonant laser pulses by a thin semiconductor films in the exciton range of spectrum at high levels of excitation, when elastic exciton-exciton interaction became effective. The film thickness is assumed to be much smaller than the lightwavelength, but much larger than the exciton radius. The process of transmission of ultrashort pulses by the thin semiconductor films is treated taking into account the exciton-photon and exciton-exciton interactions. We assume that the crystal contains only one macro-filled mode of coherent excitons and photons. We use a semiclassical approach, with the medium described by the equation for exciton wave amplitude and the field, by the system of Maxwell equations. We consider the transmission of the chirped pulse in the sense that the rate of the phase modulation is determined selfconsistently by the amplitude of exciton wave. We have obtained the nonlinear differential equation, which describes the evolution of the excitons with the effective constant of the elastic exciton-exciton interaction g (1-a ) under the action of ultrashort pulse, where g is the usual (natural) exciton-exciton interaction constant (without field) and a is the measure of the chirping. Thus, the transmission of the phase-modulated pulses through a thin film is characterized by the selfconsisted substantial changes of the strength of the exciton-exciton coupling. At certain values of the pulse modulation parameter a , it may happen that the exciton-exciton interaction will not be observed at al, since the dynamic concentration-related shift of the exciton level will be completely compensated by the instantaneous modulation frequency, or the exciton-exciton interaction will become attractive or repulsive. A similar effect referred to as the Feshbach effect is well known in atomic and molecular physics of the BoseEinstein condensation. Transmitted pulses have the shapes, which depend on the chirping parameter.