Swollen and sore throat and phlegm are caused by inflammation of the throat. There are many causes of inflammation, including viral or bacterial infections, and inflammation caused by mycoplasma or chlamydia. Once the inflammation occurs, it will be accompanied by local redness, swelling and heat, which is a more typical manifestation of inflammation, so there will be a swollen and painful throat. In addition, the throat will also secrete some inflammatory exudate due to inflammation, and the inflammatory cells in the body will gather in the throat, and for foreign viruses or bacteria to be phagocytosed or killed, these cells will fight and die in this area, and then gather in the throat. The epithelial cells in the throat will also be shed and necrotic, and these substances will be mixed together to form phlegm, so there will be a swollen and sore throat with phlegm. You can take anti-inflammatory drugs of the Chinese class for treatment, such as Pu Di Lan Anti-inflammatory Oral Liquid.