The first step I would use to desensitize a person to a phobia of dogs is provide them with information to why dogs are not dangerous. Then I would show them videos and pictures and audio of dogs. Next I would have them go in the same room with the dog in a cage or on a leash. We would not move up to new steps/experiences until they show no reaction in the current experience. For each new experience have the person go closer to the dog. Once the person is close enough to the dog have them touch the dog, petting the dog would be the final step. Provide reinforcement after the completion of each step.