Phasers create swirling, spacey modulation by shifting phase relationships in the signal. Developed in the 1960s, they gained prominence in psychedelic rock and funk. Key models include the MXR Phase 90, Electro-Harmonix Small Stone, Boss PH-3, and Walrus Audio Lillian. Used by artists like Eddie Van Halen and David Gilmour, phasers add movement to clean and distorted tones. They’re great for funk rhythm guitar, ambient textures, or thickening lead tones with dynamic modulation.