More on the National Review's take that Phillips's account is a lie.
Having seen several videos, including the 1 hour 46 minute one, which is mainly notable for how long and loud the Black Israelite guy could rant and how many fights he could pick with how many kinds of people in a short time, I think that there was probably a misunderstanding on Phillips's part.
He probably didn't see the hour preceding the events (you can hear the drums in the distance), so he must have first become aware of a mass of a hundred young men shouting and laughing and jumping around. It may have been irking to find that the noise was taking attention away from the rally. Then he saw the youths start to all squat as if they were planning mischief (probably just a big synchronized jump but he didn't know that). So he marched up to them, crooning and banging his drum. Why not use words? I guess that was not his way, and anyway there was so much shouting going on.
How was the behavior of the Covington youths? I'm not sure if the young men were collected at that spot and doing their chants there because they had to wait for their bus exactly there and were bored, or because it was amusing to tweak the all too excitable Black Hebrew guys. It seemed like the kid who took off his shirt was taunting them. Sandmann isn't doing anything worse than standing purposefully in Phillips's way and smirking a little... disrespectful, but disrespect and smirking is what teen boys do. The crowd of youths surrounds the Native Americans. The only voice I could make out with clarity during the Phillips/Sandmann encounter is the angry Native American telling the kids to "go back to Europe" (not good) though in response to what I don't know.
It looks to me as if Phillips is trying to talk to Sandmann with his drum; Sandmann eventually stops smirking and moves away for Phillips to continue his walk.
It's hard to hear their individual voices in the videos... probably most were just chanting their school songs, maybe some were saying hateful things, which would not be surprising in a group of teens. Did they say "Build that wall?" Not implausible given their politics, although it would have been a stupid thing to say to Native Americans, but the videos don't support it... nor do they rule it out.
Lest we let them all off the hook, though, the recorded behavior of at least one young man in the crowd present was very offensive.
https://twitter.com/girlsreallyrule/status/1087835791269814272