You're not blocking because you don't know how to breath correctly. You block because you don't want to stutter. It's honestly that simple, even if it feels more complex. Also they don't cramp up, you are shutting them. It may have become so ingrained that it's now automatic, but it's learned action you can unlearned. Breathing in a different way isn't going to do anything to address the issue of locking your vocal cords because you're afraid to make a stuttered sound (or one that won't sound how you want it to sound)