Drink plenty of water: When the body is hydrated, phlegm becomes thinner and can be expelled easily. Drinking lukewarm water is more effective.
Steam inhalation: Taking a bowl of hot water and placing a towel over your head and inhaling the steam can help clear the airways and loosen phlegm. (Note: Make sure the heat is not too high).
https://youtu.be/LKUNjSgGzng
Gargle with salt water: Gargling with lukewarm salt water is great for reducing phlegm in the throat and getting rid of infections.
Ginger, honey, basil: Adding a little honey to ginger juice can help reduce throat discomfort and phlegm. Boiling water with basil and drinking it is also good.
Avoid smoking: Smoking and inhaling smoke can increase phlegm. So avoid smoking completely.
Healthy diet: Fried and cold foods in oil are likely to increase phlegm. So eat hot foods.
https://youtu.be/LKUNjSgGzng
Sleep with your head elevated: Keeping your head slightly elevated while sleeping can help prevent mucus from accumulating in the airways.