Herein we introduce a facile, solution‐phase protocol to modify the Lewis basic surface of few‐layer black phosphorus (bP) and demonstrate its effectiveness at providing ambient stability and tuning of electronic properties. Commercially available group 13 Lewis acids that range in electrophilicity, steric bulk, and Pearson hard/soft‐ness are evaluated. The nature of the interaction between the Lewis acids and the bP lattice is investigated using a range of microscopic (optical, atomic force, scanning electron) and spectroscopic (energy dispersive, X‐ray photoelectron) methods. Al and Ga halides are most effective at preventing ambient degradation of bP (>84 h for AlBr₃), and the resulting field‐effect transistors show excellent IV characteristics, photocurrent, and current stability, and are significantly p‐doped. This protocol, chemically matched to bP and compatible with device fabrication, opens a path for deterministic and persistent tuning of the electronic properties in bP.