Yes, AMPHIBIANS is a Scrabble word!

Letter values in Scrabble US: A 1, M 3, P 3, H 4, I 1, B 3, I 1, A 1, N 1, S 1.

Is it a valid word?

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

a flat-bottomed motor vehicle that can travel on land or water
an airplane designed to take off and land on water
cold-blooded vertebrate typically living on land but breeding in water; aquatic larvae undergo metamorphosis into adult form

Also: amphibious vehicle, amphibious aircraft.