Henry was very wrong to do what he did or a few good reasons. First off, I am well aware that there are some people who A think that a performer doing this will send a message, and B will automatically blame the cell phone user for the kind of action Henry did. And also some may say the ushers weren't doing their job. But, there are some very important things one has to realize from a working FOH standpoint.
First off, from the second he grabbed the person's phone, any damage or issue will be Henry's fault since the phone, no matter how he got it was not his to begin with and if there was damage, like I said it would be on the part of Henry not the guy using the phone. Hell, if someone has mobil tickets on their phone, when they come up to me I am not allowed to touch their phone for the same reason. Say I'm working a Shubert house, the onus of the issue would be on me rather than them since they handed me their phones.
Also, (and this mostly applies to Broadway) different production staff has their own rules about how to stop cell phone use. Yes, for the most part if an usher sees someone with a phone out, we go and stop them. But, that isn't aways the case. Take Beetlejuice for an example. We aren't allowed to run down the aisle to stop phone usage of any kind. The production doesn't want us running up and downtime aisle during the show. Also, they tell us when late seating can happen too. Seeing that that's what they want, then that's what we do. It doesn't fall on deaf ears but we can't do much about it. I just used Beetlejuice as an example that first came to mind not the same for all shows we still have follow the production's request. So, it would be wrong to say that ushers are't doing their job etc.