Colloidal lead halide perovskite nanocrystals (LHP NCs) are promising semiconductor materials for optoelectronic devices, but the high ionicity of LHP NCs makes their crystallization control and post-treatment difficult. Here, phosphonic acids (PAs) are employed as ligands to design a solid-liquid heterogeneous reaction system to regulate the LHP NC crystallization and achieve the desired focusing growth. During the heterogeneous synthesis, the precursors in the liquid phase are responsible for the burst nucleation and initial growth of NCs. Afterwards, the focusing growth of NCs is supported by the precursors released from the solid phase. In addition, the strong binding ability of PAs enables effective passivation of LHP NCs. Without post-treatment, gram-scale monodisperse CsPbBr NCs having photoluminescence with a full width at half-maximum of 18 nm and a quantum yield of near-unity are obtained. The CsPbBr NCs covered by a compact ligand layer keep initial quantum yield even after 18 cycles of purification, exhibiting excellent stability against polar solvents, ultraviolet irradiation and heat treatment. As scintillators, the prepared CsPbBr NCs show strong radioluminescence emission and high-resolution X-ray imaging.