Listen to audio books and music through your phone's earpiece when you don't have earphones handy. Earpiece Speaker Volume Booster - speaker fix boost your audio through earpiece speaker.

Earpiece Speaker Volume booster - speaker fix is a simple light-weight audio-control app.

From Call Volume Increaser you can enable an experimental feature which switches the phone to
call volume booster phone when it's away from the face and then back to speaker phone close up. This only works on devices with a proximity sensor of course.

Another experimental feature is that you can significantly reduce the volume of the camera sounds on some devices. Ensure your local laws allow you to do this.

Earpiece Speaker Volume booster - speaker fix is free earpiece speaker app

USE Earpiece Speaker Volume booster - speaker fix AT YOUR OWN RISK. Playing audio at high volumes especially for a prolonged amount of time can damage earpiece speakers and/or hearing.

Earpiece Speaker test can also be done by this Earpiece Speaker Volume booster - speaker fix call volume increaser app.
Earpiece's audio boost option instead.