This study investigates the mechanical properties of 2D phosphorene and few-layer black phosphorus using first principles density functional theory (DFT) calculations. The results show that monolayer phosphorene can sustain tensile strain up to 27% and 30% in the zigzag and armchair directions, respectively, with a critical strain of 30%. The superior flexibility of phosphorene is attributed to its unique puckered crystal structure, which allows for significant stretching of the pucker rather than extending the P-P bond lengths. The Young's modulus of phosphorene in the armchair direction is significantly lower than that of graphene, making it more suitable for large-magnitude-strain engineering. The anisotropic nature of phosphorene is also explored, with the Young's modulus varying significantly along different directions. The study provides a detailed analysis of the strain-stress relation, elastic constants, and Poisson's ratios, highlighting the potential of phosphorene in various applications.This study investigates the mechanical properties of 2D phosphorene and few-layer black phosphorus using first principles density functional theory (DFT) calculations. The results show that monolayer phosphorene can sustain tensile strain up to 27% and 30% in the zigzag and armchair directions, respectively, with a critical strain of 30%. The superior flexibility of phosphorene is attributed to its unique puckered crystal structure, which allows for significant stretching of the pucker rather than extending the P-P bond lengths. The Young's modulus of phosphorene in the armchair direction is significantly lower than that of graphene, making it more suitable for large-magnitude-strain engineering. The anisotropic nature of phosphorene is also explored, with the Young's modulus varying significantly along different directions. The study provides a detailed analysis of the strain-stress relation, elastic constants, and Poisson's ratios, highlighting the potential of phosphorene in various applications.