A 28-year-old man from Mumbai presents with a lifelong fear of dogs that has intensified over the past 6 months. He reports that whenever he encounters a dog, he experiences sudden onset palpitations, sweating, trembling, and an overwhelming urge to flee. He avoids parks, streets with dogs, and friends' homes with pets. His anxiety is confined to the presence of dogs; he denies panic attacks in other situations. He acknowledges that his fear is excessive and irrational but feels unable to control it. His occupational and social functioning are significantly impaired. What is the most appropriate first-line treatment?