Phobia is a stable and irrational fear of certain situations, places, objects of city infrastructure, animals. For instance, fear of public speech, fear of flying, fear of acquaintance, fear of dogs, fear of being in open public place, etc. There are hundreds of various phobias and fears.
Phobias occur after traumatic experience that took place earlier in the past. Sometimes one can get a phobia just being around a dangerous, shocking situation, only observing it. It might happen that experience received in the past had been traumatic and overwhelming. It was too much to process, as a result occurs stable fear with certain body reactions, such as, tension, consternation, labored breathing, strong heartbeating, sweating, etc.
Working with a psychotherapist helps your psyche to process fear and to get rid of it. You will be able to process traumatic experience in a safe, reliable and warm environment. After that fears go away. Usually they are forgotten. You may remember that you used to fear something, but instead of feeling fear you will feel peacefulness.