To me it looks more like he is simply out of uniform. The brown shirt is his uniform undershirt, and if you look at his foot, it looks like a uniform trouser bloused into a combat boot.

I think that what looks like a collar is something hanging around his neck, or a cloth covering it (protection from the sun or to soak up sweat), or even the bunched-up collar of his undershirt.

Except for the way he is holding his hand I can't think of any reason to think he is talking on a cell phone except that this would explain why he is not covering his other ear (or perhaps he has only one arm--not uncommon among armies that fight a lot, though it begs the question of why in that case he would serve in a "combat" unit).

It may be that this unit communicates with its headquarters using cell phones, or he is actually holding some sort of tactical radio and got caught off guard when the mortar fired--which explains the grimace that indeed looks an awful lot like a smile.

Since I know that troops often operate without uniform shirts, especially when it is hot (and they lack discipline), this seems a simpler explanation than "some guy with a brown golf shirt was talking on a cell phone during a mortar firing operation").

Nonetheless, it doesn't help that the guy looks a lot like George Clooney. Just goes to show how two people looking at the same photo see different things.

George Clooney?

Mayhaps he's the local munitions rep?. He must be deaf in his left ear.

Now I am not an artillery guy, or even an Army guy (Go Air Force!), but I am not sure why all the other troops are covering their ears. Small mortars don't make that much noise when they fire. We are not talking about big howitzers here! ;-)

That might be Mr. Black or Mr. White, or perhaps Mr. Schwartz or Mr. Cohan. Those gentleman are known to travel widely and provide advice in such situations.