I don't think phenolic is used today except in very limited circumstances where there's a requirement for it. For the most part, what's used today is a material called FR4, it's a fiberglas/resin board and looks translucent yellowish or greenish when the copper is removed. Other kinds of boards include ceramic and aluminum substrate, but those are extremely specialized in nature. https://www.tempoautomation.com/blog/is-fr4-the-best-board-material-for-your-design/#:~:text=What%20is%20FR4%3F,top%20and%20bottom%20copper%20layers.