What is the term for the classical conditioning technique that involves gradual, hierarchical exposure to a feared situation or object in a real or imagined way

Systematic desensitization.

Explanation:

Systematic desensitization refers to a psychological treatment that includes relaxation techniques, anxiety hierarchy development and gradual exposure to the feared item or situation. Such treatment seeks to suppress a phobia's fear response, and gradually replace a calming response to the conditioned stimulation with counter conditioning. The relaxation training may include gradual relaxation of the muscle, calming sights, and sounds, and/or guided imaging.