One side of my throat is swollen, hard/painful to swallow, lately i have been coughing up phlegm?

Sounds like a virus: Or possible a bacterial infection. Sometimes it's difficult to distinguish between the two. It sounds like a pharyngitis, or inflammation of the back of your mouth/throat. This inflammation or swelling, is often accompanied by increased mucous production. That would account for your phlegm. A medical exam could help determine the treatment for your symptoms.