This study investigates the mechanical properties of monolayer phosphorene and few-layer black phosphorus using first-principles density functional theory (DFT) calculations. The results show that phosphorene exhibits superior mechanical flexibility compared to other 2D materials like graphene, MoS₂, and BN. Monolayer phosphorene can withstand tensile strain up to 27% in the zigzag direction and 30% in the armchair direction, while few-layer black phosphorus can sustain up to 32% strain. The unique puckered crystal structure of phosphorene allows it to tolerate large strains without significant extension of P-P bond lengths, as the tensile strain in the armchair direction flattens the pucker rather than stretching the bonds. The critical strain is determined as the strain at which the ideal strength is reached, with phosphorene showing a critical strain of 27% in the zigzag and 30% in the armchair direction. The Young's modulus of phosphorene is significantly smaller than that of graphene, with values of 0.166 TPa (zigzag) and 0.044 TPa (armchair), making it highly suitable for large-strain engineering applications. The material also exhibits strong anisotropy, with the Young's modulus in the zigzag direction being about four times larger than in the armchair direction. A general model was derived to calculate the Young's modulus in any direction for 2D materials. The study also calculated other mechanical properties, including elastic constants, shear modulus, and Poisson's ratio, showing that phosphorene has a much smaller Young's modulus compared to other 2D materials, which is attributed to weaker P-P bond strength and compromised dihedral angles. The results highlight the exceptional mechanical flexibility and anisotropic properties of phosphorene, making it a promising candidate for applications in flexible electronics and strain engineering.This study investigates the mechanical properties of monolayer phosphorene and few-layer black phosphorus using first-principles density functional theory (DFT) calculations. The results show that phosphorene exhibits superior mechanical flexibility compared to other 2D materials like graphene, MoS₂, and BN. Monolayer phosphorene can withstand tensile strain up to 27% in the zigzag direction and 30% in the armchair direction, while few-layer black phosphorus can sustain up to 32% strain. The unique puckered crystal structure of phosphorene allows it to tolerate large strains without significant extension of P-P bond lengths, as the tensile strain in the armchair direction flattens the pucker rather than stretching the bonds. The critical strain is determined as the strain at which the ideal strength is reached, with phosphorene showing a critical strain of 27% in the zigzag and 30% in the armchair direction. The Young's modulus of phosphorene is significantly smaller than that of graphene, with values of 0.166 TPa (zigzag) and 0.044 TPa (armchair), making it highly suitable for large-strain engineering applications. The material also exhibits strong anisotropy, with the Young's modulus in the zigzag direction being about four times larger than in the armchair direction. A general model was derived to calculate the Young's modulus in any direction for 2D materials. The study also calculated other mechanical properties, including elastic constants, shear modulus, and Poisson's ratio, showing that phosphorene has a much smaller Young's modulus compared to other 2D materials, which is attributed to weaker P-P bond strength and compromised dihedral angles. The results highlight the exceptional mechanical flexibility and anisotropic properties of phosphorene, making it a promising candidate for applications in flexible electronics and strain engineering.