Disc or Lettuce Coral (Turbinaria mesenterina)
Coconut Garden, Lembeh.
I have corrected sp based on appearance here:
"Turbinaria mesenterina", commonly known as disc coral, is a species of colonial stony coral in the family Dendrophylliidae. It is native to the Indo-Pacific region. The International Union for Conservation of Nature has rated its conservation status as being "vulnerable".