A challenge in 2D materials engineering is to find a nanodevice that is capable of detecting and distinguishing gas molecules through an electrical signal. Herein, the B-doped carbon phosphide monolayer (B-doped γ-CP) was explored as a gas sensor through a combination of density functional theory (DFT) and the non-equilibrium Green's function (NEGF). Formation of the B-doped system is governed by an exothermic process, and the doping increases bands crossing at the Fermi level, contributing to an increment in the number of transmission channels compared with the undoped system. The interaction between the nanodevice and each gas molecule (CO, CO2, NO, and NH3) was explored. The electronic transmission is characteristically modulated by each target molecule, enabling each to be distinguished through the conductance change in the material. Our finds propose B-doped γ-CP as a promising candidate for use in highly sensitive and selective gas nanosensors.