If it's claustrophobia this won't help but I'm always

comforted by the thought that the pilots aren't doing this to crash the plane and they've been through thousands and thousands of flights either through real life or the simulator.

I don't know if it would work but one thing that makes me comfortable on jets is the fact that I've flown in small 4/6 seat prop planes. I took a flying class in high school to earn extra credit but it was a really good experience and really lets you feel like you're flying instead of feeling like you're trapped in a tube helpless. This could have the opposite effect you're looking for but it definitely helps me during turbulent times.

I have also heard others say to equate bumps in the air to potholes or bumps on the road. Also, up in the air you don't have to worry about some dipshit next to you texting and causing accidents.