Lot of iPhone 6 and iPhone 6 Plus users reported volume issues when using the iPhone. Volume for both phone and speakers are too low. Some times when user hit volume down button once, volume is depleted to zero. Even if users tap the volume up button, it still down goes to zero.
Some times volume indicator disappears. The only way to get volume indicator back is restarting the phone.
Some times volume is too loud when users play music.
Remove protective plastic that came on the screen. Actually its is not a screen protector. Its a shipping / packing material which covers the speaker at the ear.
Go to Settings -> General -> Accessibility -> Hearing Aids and turn on ‘Hearing Aids’. It will increase speaker volume. But it will automatically turn off ‘Phone Noise Cancellation’ which is set to On by default in iOS 8.
Go to Settings -> Sound. Find a volume sound bar with slider under ‘ringtones and alerts’. Disable ‘change with buttons’ and increase external volume.
Reset all settings.
check if your phone have any 3rd party screen saver and it might covering ports. Peel it.
Blowing into the connector might solve the volume problem.
If you knew any other solutions, do let us via comment.