Why has the VOLUME decreased on iPhone 5

I used to be able to turn my music up, and blank out all other sound around me.
Now - I turn it up to the HIGHEST bar of volume, and can still hear the person chatting away next to me on the train.

The volume bars on the iPhone increase until they reach RED.
Red = DANGEROUSLY loud.

I go one bar under red, and hear nothing at all. Its only when I hit red, I begin to actually hear music. Meaning there's absolute silence on the entire 'white' bars.

WHAT THE HELL IS GOING ON?

Is anyone else's iPhone doing this?
(its not the headphones - they work absolutely fine in my laptop)

I'm on a train, and turn my phone to its highest.yet STILL struggle to hear the music.

Has something happened to the iPhone during update?

You seem to indicate that the problem has arisen after an update? If you think it hasn't worked since then, i would strongly suggest you take it into Apple for further diagnostics.
Otherwise, the only thing I can think of is perhaps your speaker is on its way out. Either way, I would have it checked out since I assume you are running the latest software.

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