Yes, PHILOSOPHY is a Scrabble word!

Letter values in Scrabble US: P 3, H 4, I 1, L 1, O 1, S 1, O 1, P 3, H 4, Y 4.

Is it a valid word?

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

a belief (or system of beliefs) accepted as authoritative by some group or school
the rational investigation of questions about existence and knowledge and ethics
any personal belief about how to live or how to deal with a situation

Also: philosophical system, school of thought.