The phase behavior of mixtures of two monodisperse diblock copolymers made up of A and B monomer units is investigated using self-consistent mean-field theory. A new scheme for phase structure analysis, namely, a "phase cube", is introduced and used to study the global symmetries with respect to the chemical compositions and the volumes fractions of the two components. Within the global scheme local density profiles for selected structures and molecular parameters are calculated and used to study the self-organization of the polymer chains. Several particularly interesting structures, such as the bilayer and inverted spherical phases, are investigated. Some possible uses for the inverted spherical phase in local thermodynamic equilibrium with polymeric components different from the A and B blocks of the copolymers are suggested.