Hi dark-hood456,
This is where it gets tricky. If you have iMovie set to sync with iCloud, then your backup will not contain that info. What does iCloud back up? - Apple Support
Here's how to verify if you do:
1. Go to Settings
2. Tap your name
3. Tap iCloud
4. Under "Apps Using iCloud" tap Show All
5. Scroll to see if iMovie was enabled
If it was not enabled, and you have a backup from before the iMovie project was deleted, you should then be able to get it with the restore.
The same goes for your Photos app, and any other iCloud enabled apps. Those that have iCloud enabled, you would enable again after the backup is restored. Then keep your iPhone connected to Wi-Fi and power until iCloud finished syncing all the info back. It may take some time, depending on the quantity and Wi-Fi network speed.
Another thought, looking at this page:Work with projects in iMovie on iPad - Apple Support
Even though, it says iPad, we see to check your Photos app for the original video. Unless, that is where you deleted it from.
All the best.