Dylan is suffering from arachnophobia. His therapist first has him go through relaxation training, and then has him construct a fear hierarchy. Finally, the therapist has Dylan go through a phase of graded pairings of spiders and relaxation responses. This approach is called:

Systematic desensitization

Explanation:

Systemic desensitization is a technique used in the field of psychology to make patients overcome their fears. First the patient is taught relaxation techniques like meditation and deep breathing. They are then told to identify their specific fears and each type of fear is ranked according to the severity. In the end both the steps are combined. The patient is given the fear stimulus and also told to simultaneously use the relaxation techniques. Gradually the fear stimulus level is increased so that the patient  gets enough time and exposure to get desensitized to it. All these steps were also used by Dylan's therapist to reduce his fear of spiders. So, systemic desensitization approach was used to treat him.

that is correct.