What are some composers in the style of Philip Glass?

You might enjoy Keith Jarret.

Have you heard The Michael Nyman Band? Chasing Sheep is Best Left to Shepherds is an interesting track to begin with. Not a piano piece in this case, but it’s as minimal in style as Glass and Nyman has written much more besides, including the musical soundtrack to The Piano.

Go to Pandora.com and create a Phillip Glass station.

What you’re interested in is postmodern minimalist style of music. My two favorites are Arvo Part and Henryk Gorecki, although they are more notable for choral work than piano. You also might check out Steve Reich.