Hey debbyf2001,
It appears that you're unable to hear the sound from videos on Facebook or Instagram, and we're glad to provide assistance.
Restart your iPhone - Apple Support -- If you haven't already tried, see if restarting your iPhone resolves the issue.
Update your iPhone, iPad, or iPod touch - Apple Support -- If you're still not hearing sound from videos in the apps that you've mentioned, make sure your iPhone is up to date. The current iOS version is 15.1. You can find this under Settings > General > About.
If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open - Apple Support -- If your iPhone was already up to date, or updating didn't resolve the issue, work through the steps in this article.
Feel free to get back to us with any questions or problems you may have.
All the best.