My iphone 6 only works on speaker when making calls

Hello there, devotion.

It sounds like you're having issues hearing callers without using the speaker function on your iPhone 6. The following Knowledge Base article offers up some great recommendations for troubleshooting:

If you can't hear a person on a call or voicemail or if the sound quality is poor on iPhone - Apple Support

Turn up the volume

While you're on a call, adjust the volume with the volume buttons:

Also while you're on a call, make sure that you can see the volume indicator on the screen when you press the volume buttons:

Check the connections

If your iPhone is connected to a headset, you won't be able to hear through the iPhone receiver or using speakerphone. Follow these steps, testing after each.

1. Make sure that you don't have anything plugged in to the headphone jack or the dock connector.
2. Go to Settings > Bluetooth and turn off Bluetooth.

Clear the receiver

The iPhone receiver won't work properly if it's blocked or dirty. Here's where the receiver is:

Follow these steps, testing after each:

• Make sure nothing is blocking the receiver, such as a case or film.
  If you have a new iPhone, remove the plastic film on the front and back of the device.
• Check the receiver opening to see if it's blocked or dirty. If necessary, clean the receiver opening with a clean, small, dry, soft-bristled brush.
• While you're on a call, turn on speakerphone. If you still can't hear, then your network or reception could be the issue. Try calling again later or from a different location.

Restart and update

1. Restart your iPhone and test again.
2. If there's still no sound or poor sound quality, update to the latest version of iOS.

Get more help

If you've tried these steps and there's still no sound or poor sound quality from your iPhone, contact Apple Support.

Thanks for being a part of Apple Support Communities.

Cheers.