Hi I have a very runny nose of a night and the next morning have a lot of phlegm which is stuck is my throat which I start to cough up?

Ongoing problem? I suspect this has been going on for awhile? Otherwise, likely a cold. Runny nose with post-nasal drip (rhinitis) can have several allergic and non-allergic (mucosal atrophy, medication effect, irritant exposure, infection, structural nasal/sinus prombelm, etc) causes. The key to effective treatment is to identify the cause. Saline irrigation is noninvasive and sometimes very effective first step.