I don’t believe that this is a significant concern. In crowded spaces, people bump into each other. And when someone by accident brushes up against someone else’s rear or chest or other intimate area, that someone almost always immediately pulls back their hands and apologizes profusely, which makes it clear that it was an accident. In your scenario, Phil’s reaction would be immediate and show emabarassment and he’d pull back and apologize, and Mary would almost certainly recognize that this was an accident and brush it off. That we’re more concerned now about sexual assault and harassment doesn’t make it more likely that Mary wouldn’t accept his apology, or realize it was an accident, ISTM.
You are missing that there are a lot of people who strongly disagree with a definition that you just presented as if it was obvious.
There are many MANY people who believe that “hands on” without excessive force would rarely if ever qualify as assault, and some of the same people would say that language (of any kind whatsoever) might be bad but is definitely never an assault.