The FoS entry for Phellinus ferruginosus (vol 2 , p257) gives spores as
Spores elliptical, smooth, hyaline, sometimes with drops, 4.5-5.5 x 3-3.5 um
Similar resupinate species growing on hardwoods are Phellinus ferreus(Pers.)
Bourd.&Galz.,usually on Quercus(oak) and with narrowly cylindrical spores
6-7.5 x 2-2.5um
So if you have spores that may help to confirm it.