I was terrified of dogs as a child until high school.
A friend of mine had this large Burmese Mountain dog and my BFF and I both went with their family on a weekend trip.
One morning I got up and went out to the living room of the cabin we were staying in. The dog approached me and I don't know what possessed me, what changed but I calmly pet her.
That was it, gradually my fear disappeared from that point.
I now own two dogs.