This doesn't address the anxiety part, but there are so many remote jobs now. He should address this with his doctor, but in the meantime, he could still have a job and work from home.
If the issue only occurs when he is driving, or otherwise away from easy access to a bathroom, the cause is unlikely to be physical. A counselor is the appropriate route, and the guess about what a counselor would tell him to do is just that - a guess.
If the anxiety stems from fear of not being able to access a bathroom, he might consider wearing an adult diaper while driving. Perhaps having a back-up plan in CASE he really had to go would help him relax.