In this work the influence of the interphase region in a three-phase magneto-electro-elastic composite material on the energy harvesting characteristics of a vibration based cantilever beam is studied analytically. The three-phase composite made of Barium Titanate/Terfenol-D/Cobalt Ferrite with different interphase regions have been considered for the evaluation. The mathematical expressions for the coupled governing equations are derived through a lumped parameter model in conjunction with Gauss's Law, Newton's Law and Faraday's Law. The generated electric and magnetic potential are harvested through the surface electrodes and a wound coil. The numerical results suggest that the interphase volume fraction and composition adversely affect the coupled material properties, which in turn significantly alters the output response of the energy harvester. Also, the lower values of resistance and number of turns of coil have a predominant effect on the energy harvester's performance. The results of this work demonstrate the significance of the interphase region and its effects on the coupled energy harvesting behavior in multifunctional composite materials.