Monolayered carbon phosphide (CP), with semi-metallic electrical conductivity and graphene-like Dirac cone responses, has attracted significant attention from the advanced nanoelectronics community, for use in gas sensing devices. The CP monolayer exhibits semi-metallic behavior in the x-direction and semi-conducting behavior in the y-direction. With the presence of graphene-like Dirac cones, it holds highly anisotropic carrier mobility characteristics. Here, we introduce the first-principle theoretical calculations for understanding the adsorption mechanism of different gas molecules-CO, CO2, NH3, NO and NO2-on the monolayer for electronic sensing devices. The binding strengths of these gas molecules adsorbed on the CP layer are much stronger than for other reported two-dimensional materials, such as graphene, blue phosphorene, germanene, etc. Additionally, the charge transfer analysis also supported an enhanced binding strength due to the sufficient amount of charge sharing between the CP monolayer and gas molecules. We further present an extensive study about the transport properties of CP monolayer sensor devices with electrodes made out of identical materials. The transmission characteristics, the density of states, and I-V response are supported by analysis of the charge distribution of the CP monolayer upon adsorption of CO, CO2, NH3, NO and NO2. Molecules have been calculated using density functional theory and non-equilibrium Green's function. The presented theoretical investigations reveal that the CP monolayer-based device exhibits improved characteristics and could be the foundation towards constructing highly sensitive nanosensor devices.