Phlegm represents the troubles in your heart, so don't worry too much.
You just often have a lot of troubles and are not good at solving them in reality. It may be that you are not good at communicating with people, or it is not convenient to communicate with family and friends, which leads to the inner troubles that cannot be solved. The subconscious mind prompts you to help you solve your troubles in the form of dreams.
I suggest you take part in some relaxing activities, make more friends and communicate with your family and friends.