This study aims to investigate the role of aggregation of the hybrid nanocomposite particles on thermal conductivity and heat transfer of the phase change colloidal suspensions. It is observed that the incorporation of the hybrid nanocomposite particles substantially enhances thermal conductivity of such suspensions up to 42.4% and effectively reduces their freezing time by 19.5%. The predictions and the experimental results supports the fact that the aggregation of the hybrid nanocomposite particles largely involve in the eventual thermal conductivity enhancements and heat transfer of the phase change colloidal suspensions, with a sufficiently lesser effects realized from the nanoparticles Brownian motion.