Phlegm sticking in the throat may be caused by chronic pharyngitis, upper respiratory tract infection, penumbral syndrome, pharyngeal cancer, reflux pharyngitis and so on. 1. Chronic pharyngitis: bacteria, viruses and other pathogenic microorganisms repeatedly infect the mucous membrane of the pharynx for a long time, resulting in chronic inflammatory reaction of the pharyngeal mucous membrane and lymphoid follicle hyperplasia of the posterior wall of the pharynx, and so the symptom will appear. 2. Upper respiratory tract infection: viruses invade the mucous membrane of the upper respiratory tract, causing acute inflammatory reaction of the local mucous membrane, and the inflammatory secretion of the pharynx increases, so you feel phlegm sticky. 3. Stromal Syndrome: congenital developmental deformity of the stroma, such as abnormal length, position and character, causes the blood vessels and nerves around the stroma to be compressed and stimulated, which results in the symptoms of foreign body sensation and tinnitus in the throat, and the feeling of phlegm sticking in the throat. 4. Pharyngeal cancer: after malignant lesion of mucous membrane of pharynx, early localized hyperplasia will cause foreign body sensation in pharynx, so there will be phlegm sticking in pharynx, and in the middle and late stages, when occupying position is serious, there will be difficulty in swallowing and breathing. 5. Reflux laryngitis: when gastric acid and other digestive juices reflux to the throat, it corrodes and stimulates the local mucous membrane, so it feels like there is phlegm sticking to the throat. Phlegm sticking to the throat may be related to a variety of factors, it is recommended to consult a doctor for a clear diagnosis.