Howdy sarahfinabobina,
It’s great to have you in the Apple Support Communities! I gather that you’re having issues hearing yourself or others during calls. You also can’t hear sound in videos. I’m happy to provide some assistance for this issue. I was able to find a few resources that should help you troubleshoot each one of the issues you’re experiencing.
Based on your description of not being able to anyone or yourself during calls and sound during videos, please give the steps here a try: If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker
Have you noticed if this issue continues when using headphones? If you don’t know or aren’t sure, please test that out if possible.
It might also be a good idea to test out the microphones of your iPhone: If the microphones on your iPhone aren't working
Take care.