The pursuit for increasing storage capacities of metal ion batteries is directly linked with the search for technologically superior next generation electrode materials. In this context, ab-initio first-principles calculations provide the means for exploring and designing novel 2D materials that can enhance energy storage capacities. In this work, we employ density functional theory calculations to draw a rationale for graphene-like B₃P monolayer which shows high dynamical, thermal and mechanical stability. Our calculations predict larger cohesive energies of 2D B₃P monolayer as compared to the well-known 2D boron-phosphide and recently predicted borophosphene, indicating its easy experimental synthesis as a graphene-like monolayer. Using both DFT and the thermodynamic energy decomposition scheme, we show that B₃P with large lattice parameters and intrinsic metallicity is a potentially excellent 2D material for applications in energy storage devices. The results of our first-principles calculations designate B₃P as a superior anode material owing to its high theoretical capacity for both Li and Na ion batteries combined with good open-circuit voltages and low metal ion migration barriers for Li and Na ions. Furthermore, sustained metallicity and thermal stability under loaded intermediate metal ion content indicates B₃P monolayer to be a promising 2D material for extending battery operating cycles.