Sodium phosphide is the inorganic compound with the formula Na₃P. It is a black solid. It is often described as Na⁺ salt of the P³⁻ anion. Na₃P is a source of the highly reactive phosphide anion. It should not be confused with sodium phosphate, Na₃PO₄.

In addition to Na₃P, five other binary compositions of sodium and phosphorus are known: NaP, Na₃P₇, Na₃P₁₁, NaP₇, and NaP₁₅.

The compound crystallizes in a hexagonal motif, often called the sodium arsenide structure. Like K₃P, solid Na₃P features pentacoordinate P centers.

The first preparation of Na₃P was first reported in the mid-19th century. French researcher, Alexandre Baudrimont prepared sodium phosphide by treating molten sodium with phosphorus pentachloride.

Many different routes to Na₃P have been described. Due to its flammability and toxicity, Na₃P (and related salts) is often prepared and used in situ. White phosphorus is reduced by sodium-potassium alloy:

Phosphorus reacts with sodium in an autoclave at 150 °C for 5 hours to produce Na₃P.

Alternatively the reaction can be conducted at normal pressures but using a temperatures gradient to generate nonvolatile Na_xP phases (x < 3) that then react further with sodium. In some cases, an electron-transfer agent, such as naphthalene, is used. In such applications, the naphthalene forms the soluble sodium naphthalenide, which reduces the phosphorus.

Sodium phosphide is a source of the highly reactive and highly basic phosphide anion. The material is insoluble in all solvents but reacts as a slurry with acids and related electrophiles to give derivatives of the type PM₃: