We focus on estimating the influences of uniaxial tensile and shear strains on a band gap in the electronic structure of monolayer black phosphorus. To study numerically the dependence of the band gap on the deformation type and strength, we apply two approaches: the tight-binding model (with the exponential and inversely quadratic strain-induced bond-length-dependent hoppings) and the density-functional-theory-based calculations. Both approaches corroborated that phosphorene as a direct semiconductor in the unstrained state can become a semimetal at certain types and strengths of deformations. The critical values of the semiconductor-semimetal transition are different depending on approximations and model parameters.