Laser refrigeration of semiconductors is an emerging field of science with exciting possible applications, one of which is optical refrigerator operating in the sub-10 K regime. Recently, it has been shown that hybrid perovskites can exhibit laser cooling through photoluminescence (PL) up-conversion. Here, we investigate PL up-conversion in CsPbBr3 nanocrystals (NCs) using temperature-dependent, frequency-dependent, and excitation intensity-dependent up-conversion measurements. We conclude that PL up-conversion is phonon-assisted and demonstrate first observation of PL up-conversion from CsPbBr3 NCs at both the ensemble and single-NC levels. Ensemble up-conversion efficiencies are estimated to be on the order of 75% for a ΔE = 23 meV excitation detuning into the NC bandgap.