I haven’t read the TLJ novel, so is there the deleted scene with Finn and co. meet some stormtroopers inside an elevator? In that case you could tie both moments together, maybe having the trooper that talks with Finn being the first to point his gun at Phasma.
Yes, that one is in there. In fact, I’m actually considering having him be there at the tracker room when they get caught to say “I’m sorry” yet again. Cause there are a bunch of normal troopers there, and they would have been in the vicinity to get the call to surprise attack them.
The problem I had with that elevator scene before is that all troopers at this point should know about the infamous FN-2187. And the novelization explains that the walls of the elevator would cause a ricochet effect killing everyone inside. So it makes sense they would receive orders (muffled by their helmets) to hold off their attack until later.