I am pretty claustrophobic surprisingly and I fly quite a bit. You'd think I'd get over it..... LOL
I always get a window seat so I can see out, that really helps. I make sure the air is pointing right on me and going full blast.
If I have to fly coach, I get a bulkhead row or buy a second seat. I can go for about 5 - 6 hours this way in coach but that's it......
Flying internationally, I will only go business or first class. I can't fly that long without being able to get up and walk around and I need the extra "personal" space around me.
Then I get a couple of good sleeping pills and knock myself out.

It is difficult to fly with a degree of claustrophobia, but not impossible :-)