Hello olib94,
Thank you for using the Apple Support Communities. I know having an issue with videos on your iPhone is not what you expect. If I understand correctly, you are unable to see videos taken on your iPhone in the Moments section in the Photos app on your iPhone, but you can import and play them in Photos on your Mac. Here is what I suggest to resolve this issue and get your videos back:
1. First, open the Photos app on your iPhone, tap the Albums option in the bottom right and then check the Videos folder if the missing videos are there. If they are not, that means the videos are not physically on your iPhone, which would explain why they wouldn’t be showing the Moments.
2. You can also sync the videos from Photos on your Mac to your iPhone by using iTunes on your Mac, and make sure to select the “Include videos” option in iTunes when choosing options as this article explains:
Keep your photos safely stored and up to date on all your devices
Cheers!