I have no phobias at all and I don't understand claustrophobia or agoraphobia but I know that for some people the fear is very real.
Since I worked in every sort of darkroom I guess that is a good thing I don't have it.
When we were first setting up the processors at my old job they were behind several doors that were designed to be light traps. If you needed to get behind the processor to load it you had to go through the door, close it and open the next door so no light could get in. Everyone was supposed to knock when coming from light to dark so that one person coming out did not have the door open when someone from the light side opened the door and allowed light to the back.
It was a simple system that worked unless someone just walked in. After standing in the dark for a while loading the processor you could see just a little from the pitiful little "safelight" but coming from the hall you were blind.
I was in the dark when a guy walked in without knocking. I just waited about 45 seconds and reached over and squeezed his shoulder. He screamed like Freddy Kruger was in there.
Then I found out it was a real challenge for him to even go into a room through three doors and stand in a room where he was blind.
He could have fogged many hundreds of dollars worth of work so he was in the wrong to open the door without knocking. We did the shoulder grab to teach them to knock before opening any darkroom door.