Phenidone B is widely used as a photographic developer, particularly in black-and-white film processing. It acts as a developing agent by reducing exposed silver halides to metallic silver, producing a visible image. Compared to traditional developers like hydroquinone, Phenidone B is more soluble in water and works effectively at lower concentrations, making it ideal for use in combination with other developers to enhance image contrast and reduce development time.

It is especially valued in fine-grain developing formulas, where it helps produce high-quality images with minimal graininess. Phenidone B is also known for its stability in alkaline solutions and its ability to perform consistently across a range of temperatures, which makes it suitable for both amateur and professional darkroom applications. Additionally, it is less toxic and more environmentally friendly than some older developing agents, contributing to its preference in modern photographic chemistry.