Yes, MULTIPHASE is a Scrabble word!

Letter values in Scrabble US: M 3, U 1, L 1, T 1, I 1, P 3, H 4, A 1, S 1, E 1.

Is it a valid word?

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

of an electrical system that uses or generates two or more alternating voltages of the same frequency but differing in phase angle