Phenolphthalein is widely used as a pH indicator in various laboratory experiments and titration processes. In acidic or neutral solutions, it remains colorless, but it turns a distinct pink or magenta color in basic solutions, typically around pH 8.2 to 10. This property makes it invaluable for determining the endpoint in acid-base titrations, particularly in educational and analytical chemistry settings.

It has also been historically used in medical applications as a laxative, though this use has declined due to safety concerns and the availability of safer alternatives. Additionally, phenolphthalein is employed in forensic science as a presumptive test for blood, where it reacts with hemoglobin to produce a visible color change, aiding in crime scene investigations. Its versatility in both scientific and practical applications highlights its importance across multiple fields.