Hey hary99,
Thanks for posting in Apple Support Communities. We understand that you'd like to delete all photos and videos from the Photos app on your iPhone. We're happy to help.
To avoid data loss, we'd like to confirm if you have iCloud Photos enabled. To check, go to Settings > [Your Name] > iCloud > Photos. If iCloud is enabled, deleting photos from your iPhone will delete them from all devices using iCloud photo library.
If you've already deleted photos, but the space doesn't clear, check your Recently Deleted folder:
- Tap Albums, then tap Recently Deleted under Utilities.
- Tap Select, then choose the photos and videos you want to recover or delete.
- Choose Recover or Delete at the bottom of the screen.
Delete or hide photos and videos on iPhone - Apple Support
Let us know if you have any questions! Take care.