This is what happens if he follows your specific instructions. Motherfucking triangles. Yeah, you could delete each second edge, but your edgeflow is still fucked due to them all leading to a single point on each corner. There is a proper way to model that surface to keep it fully workable all over if one wants, but we won't get into that.
If he's going to go that route, he shouldn't even bother welding the corners. Simply insetting once will give him back modeling control over his outside edges. But again, if he actually wants to make this phone look realistic, he should do as I said to actually model the metal edge to its real physical shape.