Thank you for your query at AskTheDoctor.com
I understand your concern.
It could be due to allergy or could also be secondary to a bacterial infection. Not all infections manifest with a sore throat or congestion. You can do saline gargling which will loosen the mucus in the throat and it will come out easily. Also, an antibiotic course such as Amoxicillin will help to clear up the infection. You can get your throat checked by your physician and start the medicine according to his guidelines.
Sometimes such phlegm could arise due to allergies but you will also have other symptoms such as itchy throat or runny nose and sneezing. Since you did not mention any other symptoms it points more towards an infection. If you do have these symptoms, you can take an antihistaminic like Levocetirizine to reduce the phlegm.
Hope this was helpful,
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