what causes the mind to operate on fear and a person to develop phobias?
Those things come from 2 places, the self or outside the self. Past experiences that actually caused injury will create a fear of the similar thing happening.
The question is, Is it probable it will happen again? Maybe maybe not, depends on the situation.
The other is self talk. What we tell ourselves and or allow our minds and emotions to wander on.
The way to get over them is to realize that fear comes from living in the past or the future 99.9999999 percent of the time. Very few moments of our life are we actually IN danger. I have noticed that when that moment happens usually we simply react there isn't time for fear. Fear comes before and after.