Claustrophobia is related to anxiety, as a matter of fact, phobia of anything generally results in anxiety. Claustrophobia is a type of anxiety disorder whereby someone tends to have an extreme or intense fear of enclosed spaces or fear of being put into a small place where it seems there is no escape route.
Anxiety is a state of mental uneasiness, nervousness or a form of mental apprehension. Claustrophobia is regarded as an anxiety disorder because when someone who is claustrophobic is confronted with things that usually prompt his fear like being locked up in a room for several hours, getting stuck in a very crowded space, there would be a kind of mental apprehension due to the intense fear that has filled up his mind.
What phobia generally does to people is to make them very anxious and fear will start coming in, when this becomes too much, it can lead to many complications.