Yes, PHASE is a Scrabble word!

Letter values in Scrabble US: P 3, H 4, A 1, S 1, E 1.

Is it a valid word?

PHASE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

any distinct time period in a sequence of events
(physical chemistry) a distinct state of matter in a system; matter that is identical in chemical composition and physical state and separated from other material by the phase boundary
a particular point in the time of a cycle; measured from some arbitrary zero and expressed as an angle
(astronomy) the particular appearance of a body's state of illumination (especially one of the recurring shapes of the part of Earth's moon that is illuminated by the sun)

PHASE was the Wordle answer on June 3, 2022 (#349). Stuck on today’s? Use the Wordle helper.

Also: phase angle.