Claustrophobia is the fear of closed and confined spaces, from which it is difficult to escape. If you subjected to small rooms or tunnels or holes, then you invariably get anxiety attacks from the experience. Airplane cabins, especially in the economy/coach section, can be quite cramped with not much space, making it difficult to travel for someone with claustrophobia.
The obvious answer to the best airplane seat is a seat in first-class or business-class, as these seats have more room. However, many people can't afford the much higher first-class and business-class seats. The best seats on the plane if you can't afford first-class or business-class are the exit-row seats. These exit row seats have more leg room, and the seat in front of the exit row seats are moved way up to make room for an exit lane for the exit doors. Exit row seats do come with a higher fare. The next best seats on an airplane for someone with claustrophobia are the bulkhead seats, as these tend to have more legroom, and you don't have to worry about a seat in front of you reclining back into your personal space. If you can't get any of the above seats, then an aisle seat is better than a window or middle seat, as it allows you to stand up at will without having to ask anyone to move so that you can pass.
It is important to get up and walk around frequently for someone with claustrophobia. You can also visit the washroom frequently and splash some water on your face and freshen up.