The duality and other symmetry properties of the effective conductivity sigma_e of the classical two-dimensional isotropic randomly inhomogeneous heterophase systems at arbitrary number of phases N are discussed. A new approach for a obtaining sigma_e based on a duality relation is proposed. The exact values of sigma_e at some special sets of the partial parameters are found.The explicit basic solutions of the duality relation, connected with the higher moments and satisfying all necessary requirements, are found at arbitrary values of partial parameters. It is shown that one of them can describe sigma_e for systems with a finite maximal characteristic scale of the inhomogeneities in a wide range of parameters. The other solution, connected with a mean conductivity describes sigma_e of the random parquet model of N-phase randomly inhomogeneous medium in some mean field like approximation. The comparison with the known effective medium approximation and crossover to the continuous smoothly inhomogeneous case are also discussed.