Persistent throat irritation with mild cough and some phlegm can be caused by conditions such as Pharyngitis, allergies, post-nasal drip from sinus problems, or acid reflux. Drinking warm fluids, doing salt-water gargles, avoiding very cold or spicy foods, and staying well hydrated can help reduce irritation. Doctors may sometimes recommend medicines like Levocetirizine for allergies or Ambroxol to help clear phlegm.