Like DS said, there are some people out there that will never understand no matter what you do.
However, there are other people out there that can learn if someone just takes the time to show them some what it's like to have that phobia and how it affects your life.
It all depends on that person, not you. Some people are understand while others are not.
Some people may come from a town or country where most schools don't teach psychology topics like phobias, and not everyone take the time to learn about phobias by reading a book about phobia, or use the internet to learn about phobias. It maybe difficult teaching them phobias if they don't know anyone with a phobia, or almost no one in their town know anything about phobias and psychology.
There are some people with mental problems where their brain can't learn more difficult problems like phobias.
There maybe some people who just want to learn enough to survive and do basic tasks like learning how to make money, buy food, pay taxes, obey the law, drive a car, and clean, but they are not interested in scientific topics like phobias.