This is all coming from what ive read and researched, so take that into account, but there are several grades of phenolic with different applications. They make it from paper, linen, and canvas, among other things. The ones made of paper and other thin materials are more dense and can be sanded and more highly polished than the canvas or linen varieties. Modern billiard balls are made of phenolic resin.
From what I understand, most phenolics like micarta and G3 are formed under a great deal of heat and pressure. That's probably how they avoid the air pockets and make them seem so consistent.