The integration of luminescent nanoparticles into transparent polymer matrices opens the way to affordable, scalable and efficient luminescent solar concentrators. A key challenge in the fabrication is to prevent agglomeration of the nanoparticles as this will drastically reduce the performance due to scattering effects. The incompatibility of inorganic nanoparticles with organic media typically leads to irreversible agglomeration upon direct mixing. In this study, inorganic luminescent Y3Al5O12:Ce3+ nanoparticles are transferred from a polar to a nonpolar solvent without any noticeable agglomeration using amphiphilic statistical copolymers as stabilizing agents. The process parameters that determine the success of stabilization are studied both theoretically and experimentally and a general procedure is proposed to find the optimal conditions for the phase transfer process. The importance of compatibility between the amphiphilic copolymers and the polymer matrix was demonstrated by integrating the stabilized nanoparticles into various polymer matrices. Fully transparent polymer nanocomposite thin films were prepared without any sign of agglomeration. The simple, universal and scalable method presented in this report allows for the fabrication of nanocomposite luminescent solar concentrators using a wide variety of luminescent materials and polymers.