Hello Sylviaxox,
It seems you are experiencing an issue with the microphone of your iPhone. That does sound troublesome. The following article provides troubleshooting guidance which may help you find a solution:
If your voice is too faint or sounds unclear using iPhone, or iPod touch - Apple Support
Follow these steps, testing after each with Voice Memos.
- Unplug anything plugged into the headset jack.
- If you're on a call and holding your phone next to your ear, speak into the microphone and make sure you don't block it with your fingers or shoulder.
- If you're using a screen protector or case that covers the microphone, remove it. Clear any debris from the microphones.
- Restart your device.
- Update to the latest version of iOS.
If you've tried these steps and people still can't hear you well on calls, contact Apple Support.
Thank you for contributing to Apple Support Communities.
Cheers,
Bobby_D