The results of studies on the optical properties of colloidal InP/ZnS nanocrystals stabilized by a heterobifunctional polymer based on polyvinylpyrrolidone are presented. The optical absorption and photoluminescence spectra of (i) solutions containing different concentrations of nanocrystals and (ii) film samples, as well as the temperature dependences of these spectra in the range of 6.5–296 K are analyzed. An inhomogeneous broadening of the exciton optical bands was observed, which is associated with a broad size distribution of nanocrystals. It was established that the temperature-induced shift of the exciton absorption and emission maxima is mainly due to the interaction with acoustic phonons. It was shown that quenching of defect-related luminescence involves the local energy levels of the dangling bonds of phosphorus atoms at the core—shell interface, while the temperature stability of exciton emission is governed by the thickness of the ZnS shell.