I'm looking to improve my bench press and I'm having trouble about 1/4 way off my chest - can someone describe what muscles are primarily activated during each phase (break the movement down to 1/4's or 1/3's).
This article might have what you are looking for. Since I can't get in, I can't be certain. There are a couple other articles that may be of interest, but not exactly what you wanted:
That said, you may need to try a process called deloading. Essentially, cutting back 10% on the weight so you can get your full set in. Then progressively load by adding 5lbs back on each bench press session. As the theory goes, you should be able to get past the plateau that way. In short, it's taking longer for your muscles to recover than the typical 48 hours or however much rest you normally give them.
Eventually you'll get to the point where even deloading won't get you past a plateau. With the StrongLifts program you compensate by going from 5x5 (5 sets/5 reps) to 3x5 on that lift. The threshold for that is when you deload twice and it doesn't help you improve. From there you go to 1x5, and eventually transition to another routine when you've maxed out that program. I think the takeaway is that eventually you have to reduce load to increase weight on the bar.