Hello Gaga-rjgm,
If you haven't already done so, you can sign into the iCloud website on a computer to verify your photos and videos are still appearing there: iCloud Photos
If they are still appearing there, you should be able to sync your photos back to your iPhone using the steps below:
1. Go to Settings > [your name].
2. Tap iCloud.
3. Tap Photos, then tap the switch next to Sync this [device].
You can also find those steps in this resource: Set up and use iCloud Photos - Apple Support
That process can take some time to complete depending on the size of your Photos library. Staying within range of Wi-Fi is recommended.
If you run into any snags with that process, just let us know. We'll keep moving forward from there.