I’m not sure what happened. The execution was straight forward and obvious. I got that. It was photographed and I got that. Brookman sends the photo to Shaw, I got that.

Brookman makes a phone call and I don’t know to whom or why.  Personally, I like a mysterious ending that could initiate some classroom conversation and perhaps that is your objective. A teacher could give a creative writing assignment to have the students reveal who was on the other end of that call and what happens next. If that was your goal, well done. My take was that Bookman was calling the New York Mets who need a new batting coach and the pictures of Shaw show that he has a perfect swing.

I do have some advice to add. In your opening paragraph you introduce Brookman and Leary. In your second paragraph you introduce Leary. Then you describe Leary as being in a suit. You’re fine so far. Then you describe Brookman as also being in a suit. At a glance I was led to believe that Brookman and Leary came together in the same slow moving sedan. I had to re-read the first paragraph to confirm that Brookman was already there.

In short, keep your character descriptions in the same paragraph or close to their introductions. It’s a matter of organization. This way you keep the reader’s attention and they don’t start reading the next story that’s waiting in their overstuffed inbox.

Writer,

I've never listened to this song by Skynyrd until today.   This was a good effort.   To be honest, I was anticipating Shaw to slice Brookman.   I'm guessing by the ending, Brookman is fixing to double-cross Shaw?  Having Shaw use a sword for the weapon added dramatic flair to the killing, in my opinion.

All the best.

Two men are in the open field. One is standing, the other on
his knees, hands behind his back and blindfolded. The man
standing is BROOKMAN (40s). The man held captive is LEARY
(30s). (Here is where you add how both men are dressed, and also detail that Leary is bound, gagged, blindfolded)

A nondescript (no need for nondescript) sedan slowly pulls up and comes to a halt.(no need for the engine bit) or the driver's side bit)Engine shuts off. The drivers side door opens and

(Start here) SHAW (late 50s) steps out. He wears a nice suit. (Give us a bit more description of Shaw as your quintessential hitman. (Delete the wardrobe stuff for Brookman and Leary as it goes in the first para when we first see them)Brookman is also in a suit. Leary in a casual shirt and shorts. Brookman pulls the blindfold off Leary. (Maybe Shaw says something to Leary here, maybe something funny, or completely inappropriate) He's gagged also so still can't talk.
Nervous mutterings out of his mouth as the two other men
stand over him.

Your header is Open Field so you don't want to repeat open field again in your description. Give us some other description of this field that makes it stand out. Maybe there's an open grave already dug, perhaps it's such a desolate area, a barren landscape, no houses or landmarks as far as the eye can see.

So let's just say(as I think Lew mentioned) this is a scene from a bigger story (which is fine as per the parameters) - in this case you don't have the luxury of any dull moments.

You could add conflict between your standover/hitman guys. A simple way to do this is via dialogue. Look at Tarantino examples to see how he injects humour or, for example, the dichotomy of the every day with the menacing - example  in Pulp Fiction, the royale with cheese discussion.

The only other way is to inject something that comes completely from left field (no pun intended) - your guy gets loose, or a third party turns up, or the guy with his head on the chopping block drops dead from a heart attack. Maybe then Shaw still wants a photo but the guy's already dead and an argument breaks out about money, he now won't pay him cause technically it wasn't a hit etc. It's Shaw's final job and it's now ruined cause this guy dared to drop dead of natural causes

Finally, it would make more sense if the photo op is Brookman's idea, otherwise your final act is a bit too convenient. And/or as others have said, he uses his own phone otherwise he's coming across as world's dumbest criminal.

The story held my attention, it just needs more.
And you can do it!

Oh, and watch Mr Inbetween.
https://m.imdb.com/title/tt7472896/