Exterternal speaker, however if it was louder at one point and has since degraded then it may be a software glitch which can easily be solved by creating a BACKUP on either iTunes or iCloud and then restoring your phone to factory defaults from then you can restore your information on it using your backup. If this does not work and your phone is still under its warranty(1 year normal 2 year if you have AppleCare) then apple will replace your phone. Restoring your phone is apples final ace in the sleeve before they replace a device. This may also be resolved by simply updating your device.