I only cough up phlegm when i lay down , and sometimes a clear liquid comes from my nose?

Clear nasal drainage: positional cough with phlegm can be caused by several things. It could be postnasal drainage from allergies or could be a sign of more serious lung or heart issue. If it persists a doctor should examine you and listen to your heart and lungs. Clear nasal drainage could just be a sign of nasal allergies or nasal irritation. It could also be cerebrospinal fluid leaking but doubt this if no trauma