Phosphorus nanoribbons combine the tunable bandgap and high mobility with the inherent anisotropy of one-dimensional systems, offering promise for functional electronics, but their intrinsic low stability hinders practical applications. Here, we report phosphorus-lithium double-helix nanoribbons with a well-ordered helical architecture and high structural stability under harsh conditions such as in air up to 225°C, water, and even acidic solutions. Comprehensive experimental characterizations and theoretical analyses show that the stability arises from a synergistic combination of Zintl phase formation between phosphorus and lithium atoms, noncovalent interhelical interactions, and geometric protection offered by the distinctive helical architecture. The nanoribbons show tunable optical properties dependent on temperature, thickness, and polarization state. It is demonstrated that these properties enabled nanoribbon-based hydrogels with self-healability and highly efficient photothermal conversion, showing a general approach for stabilizing active low-dimensional materials and paving the way for applying phosphorus-based nanostructures in biomedical engineering and quantum technologies.