Hey, what usually happens is the speaker/earpiece grill gets filled with dust making it hard for the sound to pass through. Usually happens with old phones or heavily used phones. The same happens with charging ports and headphone jacks. Take a flashlight and shine inside, try to see if there is any build-up of dust. Your best bet is to take something thin and gently poke it out. Don’t go too deep, you can damage the speaker itself.