Chronic phlegm can be due to allergy, gastric reflux and post nasal drip
. Common food allergies are those to gluten, lactose, citrus fruits, egg, sea food, preservatives etc. Common allergens are pollen, mold, dust, pet dander, cosmetics or drugs.
Take Omeprazole empty stomach in morning and an antacid gel at bedtime. Refrain from smoking, alcohol, fuzzy drinks and spicy food. If phlegm is due to reflux, this will help you.
Among infective causes tuberculosis is a possibility.