This paper illustrates the application into the MoM technique of a clever formulation to evaluate the array Green's function (AGF) of large finite planar phased array. The procedure is based on the AGF representation in terms of a double spectral integral, whose integration paths are properly deformed to have an exponential attenuation of the integrand. The diffraction integral is evaluated numerically for point close to the array edges while an asymptotic treatment is proposed far from the edges. This latter comprises higher order contributions. Thanks to this convergence properties, the final algorithm is numerically accurate, stable and more efficient with respect to the individual element summation for large arrays. This AGF is then inserted into the MoM scheme, where the reactions are calculated between two basic cells ("cell on cell"). Each cell includes the radiating element, which is still meshed by using RWG basis function. This procedure allows a reduction of complexity either in filling the MoM matrix or in solving the system.