Psycho therapy or behavior modification techniques , which one is more effective for phobias?

Both are great: Psychotherapy can involve many forms of treatment including behavior modification. Cognitive-behavioral therapy in particular with exposure therapy is often very effective to treat phobias. See your doctor to determine the best treatment plan for you.

Behavior therapy : Behavior therapy that involves exposure to feared situations is the most effective treatment for phobias. Relaxation and imagery may be part of the exposure. The exposure is done systematically one step at a time, easier steps first and gradually more difficult ones. Numerous studies have shown that when done this way it is 80-90 % effective with simple phobias.

Agree w Dr. Altman: Cognitive Behavioral Therapy would be my first recommendation.