Look at the effect of the starting strength exercises on your back:
* Squat: the entire posterior chain is used to hold the back in a natural curve and the lats get a bit of extra work with the low bar position. However, the back is a stabilizer here and not the main mover, and most of the stress is on the lower part of the back anyway (as the bar is further away from it).
* Deadlift: similar to the squat in that the back is used to keep the back in a natural curve. However, compared to the squat there is significantly more stress on the back, as the bar is further away, you typically use more weight and the legs do less of the lifting. Again, the back's role is to stabilize and most of the focus tends to be the lower back, but the upper back will definitely see an impact.
* Bench: minimal usage of the upper back to stabilize the weight.
* Press: keeping your body upright with a weight above your head uses a lot of upper body muscles, including the upper back. Again, the role is stabilization and the effect will not be too big.
* Power cleans: getting the bar from the floor to just above the knees is a deadlift, so the same analysis applies. After that, the explosive movement uses mostly your lower body (quads, hips, lower back) to fling the weight upwards along with a shrug, which will hit your traps pretty hard. Your upper back muscles play a role in stabilizing your back, similar to the squat, but the effect is again not huge.
* Rows: the first part of the movement is your lower back/hips (just to lift the weight off the floor) but after that, it is a movement almost entirely generated by the upper back muscles - traps, rhomboids, lats - with some help from you arms/biceps and back of the shoulder. This hits your upper back very directly.
* Pull-ups/chin-ups: virtually all the work is done using your upper back (lats and rhomboids) with help from the biceps and forearms. These hit your upper back very directly.
As you can see, the exercises that directly use the upper back muscles are rows and pull-ups/chin-ups. Focus on those if you need extra development. However, I listed all the other ones so you can get an appreciation of just how much your back is doing as you do the rest of the lifts in starting strength, so don't overdo it, or you'll suffer on all your other lifts.