The chemical compound caesium phosphide is an alkali metal phosphorus compound that is extremely dangerous. The reaction of this compound with water produces phosphine gas, which is highly toxic. It also ignites combustible material such as plastics and rubber. This poisonous gas can be absorbed through the skin or inhaled. It can cause burns, and damage to the eyes and lungs. Calcium phosphide can be found in laboratories and is used to produce other chemicals. It is a greyish-white solid.

Caesium is a member of group 1 of the s-block of the periodic table. It has atomic number 55. The valency of cesium is +1, so it reacts with other elements and molecules to form compounds that have different stoichiometry. It is often combined with metals to produce metal phosphides. These are more stable than calcium phosphide.

Phosphorus is a multivalent nonmetal of the nitrogen group, and it occurs in nature in several allotropic forms. White phosphorous is the form most commonly used in industry. It glows in the dark and is easily flammable, but it is not as dangerous as the more volatile red or black phosphorous.

Phosphorous is a highly reactive element, and it has been used as an indicator in some types of industrial gas detectors. It is also a component in many flame retardants. Other uses include producing phosphorous glass and phosphate glasses, which are useful for radiation detection, nuclear energy generation, and high-temperature electrical conductivity. It is also used as a sputter target in ion beam techniques, and it acts as a cocatalyst in the hydrogen evolution reaction for production of acetylene.