The answer to this question seems to refer more to instrumental conditioning than classical conditioning. The main clinical application of classical conditioning even today is that it is the most effective treatment for phobias. The absolute best treatment for phobias is a combination of classical and instrumental conditioning, known as treatment for avoidance learning. Phobias are created because fear becomes associated with a particular stimulus. Fear is a naturally occurring response and, therefore, is an unconditioned response that becomes a conditioned response associated to a conditioned stimuli, such as spiders or snakes. The attempt to avoid fear by avoiding snakes and spiders is how phobias become a form of avoidance learning. Relaxation in the presence of the conditioned stimulus, mostly through imagery now a days, is the method used to reduce the fear response in successive approximations. Of course, there is a little more to it. Relaxation is an incompatible response to fear.