Not sure if break down is really being used phrasally here ...
You can add a preposition after a verb to indicate the direction that the activity was pointed toward. This can overlap with phrasal verbs.
I threw down the ball to Jimmy = I threw the ball in a downward direction to Jimmy, Jimmy is below me.
And sometimes the direction of the activity is specified but the subject of the activity is not directly "aiming" the action:
We broke down the wall = We destroyed the wall. We didn't necessary apply force in a downward motion but when a wall breaks it will fall down to the ground by itself.
But break down can be used to describe destruction for things other than walls:
Relations between the US and North Korea broke down.
It also can be used to not necessarily mean "to be destroyed" but something like "remove". So barriers in the sense of things that block communication are a logical type of wall and to "break them down" means to find a way through the barrier.
It also can mean to take apart in preparation to be put away:
The carnival ended, the workers broke down the tent and later loaded it on a truck.
A meaning of break down that is not related to the above, where it 100% is a phrasal verb, means to reduce to smaller parts, typically to try to understand.
This is a complicated topic, let's break it down into simpler concepts so we can understand.