It seems that you have enabled iCloud for the Photos app on your iPhone, then any changes you made on your iPhone Photos are synced with iCloud, that is to say, when you delete the photos and videos in the Photos app on your iPhone, you also remove it from your iCloud, they are unavailable on all other iCloud-synced devices.
When you find you mistakenly deleted photos and videos on your iCloud-enabled iPhone, you can recover them from the Recently Deleted album, if you have already emptied the album, you can't recover them again unless you have created an iCloud backup for those items.
