Fish don't have introverted behaviours or a egos thats really projecting human emotions onto them... you are describing a fish in a stressed state so you need to work out what is stressing them.
Phosphate wont be the answer, I've never heard of this even being a contender for fish health issues. Have you got a liquid test kit and if so can you post the ammonia, nitrite and nitrate levels.
You will need to give us more info about the set up, tanks size, age of the fish, tank mates and also some info about the scape of the tank and also the room the tank is in. If the fish is not used to people walking past the tank it wont like seeing them occasionally, or if it is in part of the house where people or kids are running around the fast actions might dart around. I've heard to people having stressed fish in rooms where there is a lot of flashing lights from TV's with films or games etc.
The scape of the tank is important because a lot of flowerhorns are kept in bare bottom tanks and while there are advantages to it for them - they often bash around because of their deformed bodies and are prone to infection because of their compromised genetics. But smooth decor with cover and shelter can really help as well.
Wills