Hi, if a restart of your iPhone hasn’t fixed the issue, you could try a ‘hard restart’ by holding the Sleep\Wake button and the Home button at the same time, until the screen shows the Apple logo. If it’s still the same after this, and you notice that when changing the volume the display says “Headphones”, then this could be due to debris in the headphone jack (hole) or water damage or some other hardware issue. Shining a torch in the hole may show up anything still stuck in there. Getting it out can be tricky as you can damage the connectors in the socket, but there are lots of web sites which have advice on this if you search for the issue. You may wish to speak to Apple Support or visit an Apple Store if you have one nearby.