I don't think anyone was seriously considering trying to hold it. My comment was more in line with "The iphone will desintegrate due to the forces involved and the shrapnel will cause serious injur". Granted, those disks can shatter and I assume an iPhone may also shatter, but saying it will is a different.
PS: I am going to leave this alone. It's dangerous, but I do hope someone posts a video of this at some point.
I have a hard time envisioning the kind of hold-down that would be required to hold a smooth iphone onto an angle grinder. That's going to be a really neat bit of engineering. And then of course the guts of the iphone will die anyway, I seriously doubt that it was designed with that kind of abuse in mind. But we can place bets on how many seconds it will last.
PS: I am going to leave this alone. It's dangerous, but I do hope someone posts a video of this at some point.