You can remove large groups of photos from an iPhone in the Photos app, but be careful if iCloud Photos is enabled. Deleting a photo on the iPhone also deletes it from other devices using the same iCloud Photos library.
- Open Photos and go to your library.
- Tap Select, then select the photos and videos you want to remove. You can drag across thumbnails to select many items quickly.
- Tap the trash button and confirm the deletion.
- To free the space immediately, open Collections > Recently Deleted, unlock the collection, select the items, and permanently delete them.
Items normally remain in Recently Deleted for 30 days unless you permanently remove them sooner. If your goal is to keep the pictures in iCloud while removing only the local copies, do not use the Delete command.