The performance of uniaxially strained phosphorene tunneling field-effect transistors (TFETs) is assessed by first-principles-based quantum mechanical simulations in this letter. Due to the highly anisotropic band structure, the devices without strain along the armchair direction (AD) show superior performance to those without strain along the zigzag direction (ZD), and the same tendency ismaintained with increasing compressive strain. However, tensile strain induces band switching between the first and second conduction subbands, where the heavy effective mass of electrons along the ZD becomes light, while the opposite is observed along the AD. Furthermore, a point on the inverted right perpendicular to X path starts to contribute dominantly to band-to-band tunneling and improves the ON-state current of ZD TFETs, which becomes comparable to that of AD TFETs. These results demonstrate that, through strain engineering, the performance gap between AD and ZD TFETs can be significantly narrowed, lessening the orientation dependence of phosphorene.