Physical damage is displayed in red in skill descriptions.
In battles, it appears in orange.
Armor decreases incoming physical damage.
Note: All heroes deal physical damage with basic attacks except Celeste, Satori, and Augustus.
Once Celeste's Zenith skill is unlocked, she starts dealing magic damage with her basic attacks while in the Dark Form.
Satori's basic attacks deal magic damage thanks to his first skill, Ravenous Pack.
Augustus' basic attacks deal magic damage when you unlock his skill Path of Least Resistance.