I’m not sure about a phenolic plate, but it seems similar enough to Richlite which is paper fibers in phenolic resin, and I have cut some of that, see this thread:
Contour cuts with that 2-flute 1/8" endmill were also 18k RPM / 45ipm / 0.5mm per pass.
That said, I was being conservative in that project, Richlite is expensive and I did not feel like experimenting to optimize cutting speed.