phalanx issue is only a problem when the boss is at an upper wall. knockback on that skill (not sure it even has knockback) would never push it upwards because the arrows shoot downward.
a lot of bosses teleport when they take damage, so tapping them in the corner can bump them out and allow you to reposition. wyrmshot is bad for bosses but if you cant get close enough for barrage safely or you cant stack phalanx nicely, then you can lure and wyrmshot and they'll usually follow or teleport out. Rapid wyrmshot is much better for single targets than regular wyrmshot. thats also why I mentioned that bit.