When you have bronchitis and cough up phlegm, is it ok when you swallow it?

If you swallow large quantities of it, it may upset your stomach, but it's not truly harmful. It will go into your stomach, not back into your respiratory system, so you will not cough it up again. The germs it may contain will usually be specific to the respiratory system, so they will not affect your digestion and will be killed by your stomach acid. All in all, though, it's still a better idea to spit it out when you can just to avoid upset stomach.