Which symptom is he exhibiting?

An obsession refers to persistent and intrusive thoughts that cause significant anxiety or distress. While obsessions can influence behavior, they are not necessarily false beliefs but rather repetitive thoughts that the individual may recognize as irrational. This distinguishes them from delusions, which are firmly held beliefs.

Hallucinations involve perceiving things that are not present, such as hearing voices or seeing things that do not exist. Unlike delusions, which are beliefs, hallucinations are sensory experiences that can occur independently of the individual's belief system. Thus, experiencing a hallucination does not imply the presence of a delusion.

A compulsion is a repetitive behavior or mental act that an individual feels driven to perform in response to an obsession or according to rigid rules. While compulsions may be associated with obsessive-compulsive disorder, they do not involve the false beliefs characteristic of delusions, making them distinct symptoms.

A phobia is an intense and irrational fear of a specific object or situation, leading to avoidance behavior. Although phobias can significantly impact a person's life, they are not based on false beliefs, but rather on exaggerated fears. Therefore, they do not align with the definition of a delusion.