Whether listening to music on your iPhone, watching a movie or making a FaceTime call, the volume coming out of the iPhone can sound muffled or muted due to low volume settings or obstructions over the speaker. If your iPhone seems quieter than usual, troubleshoot these common problems first.
If you notice a decrease in your iPhone's volume, the first thing to check is the volume setting. Press the button with the plus sign, located on the side of the iPhone, to turn the volume up all the way. Or, adjust the volume slider that appears when watching movies or listening to music. When the volume is turned all the way up, the slider is all the way to the right.
If you recently purchased a third-party phone case for your iPhone it could also contribute to the decrease in sound. Some of these cases block and muffle the speakers, making the sound seem quieter than it was previously. To prevent this from happening, inspect phone cases carefully before buying one to ensure the speakers won't be covered completely. Use a case that's designed for your iPhone model, as the size and speaker location vary depending on which iPhone you own.
Inspect the speakers closely to ensure they're not being clogged by dirt, dust or food particles -- all of which can lower the iPhone volume. To clean the speakers, use a small, stiff brush and gently brush the mesh filter that covers each speaker. Never use a liquid cleanser on the speakers, as it can get under the mesh filter and cause permanent damage.