Does your speaker work Ok if taking a phone call that way ?
if so my suggestion is to try closing the app and relaunch it.
If no joy then try turning the iPhone off and on.
If no joy then try a soft reset by holding the home and power button in until the apple logo appears and let go. The process is slightly different for newer iPhones with the different style home button.
You could also try the reset settings options in the iPhone.
If no joy then if you have an Apple Store local pop in and they'll look at it for you.
Or a Vodafone Highstreet Store can look st it and send it off if necessary. Make a back up if they do want to send it off of your information and take time and date stamped pictures of your iPhone with one of it turned on and if you can one of the water sensor just inside the SIM card slot.
Current Phone >
Samsung Galaxy s²⁴ Ultra 512gb.
