Hello Dear. A thick and green phlegm may be a sign of a viral or bacterial infection, sinus infection, or lower respiratory tract infection. Typically, this occurs when the immune system sends white blood cells, known as neutrophils, to the area of infection. These cells contain a green protein, which, when present in large quantities, turn the mucus into a greenish hue. If you are not cured even after several doses of oral antibiotics then chest xray may be required to see if you have pneumonia. In that case the doctor may suggest you to get admitted and get a course of IV antibiotic. The doctor may also send your sputum sample for testing for Tuberculosis. Hope i have answered your question. Feel free to contact me if you have any more questions. I ll be glad to help you. All the best With warm regards Dr Sanjay Kini