Is there a way to delete photos from my iPhone without deleting photos from iCloud photos?
No, as far as I know, there's no way to do that using iCloud, they're always kept in sync. You can either:
- Ask Apple to change this behaviour: http://www.apple.com/feedback/
- Use a different cloud service, e.g. OneDrive, Dropbox or Google Drive, they all provide a way to backup your photos and sync them for offline viewing when needed.
Photos in the Camera Roll folder are the photos stored on your phone. Deleting them won't affect the photos uploaded on iCloud. However, you may want to check if your latest photos in the Camera Roll have already been uploaded on iCloud by checking the My Photo Stream folder. The My Photo Stream folder is the one synced throughout your devices.
In iOS, tap Settings > iCloud > Photos or Settings > Photos & Camera, then select a storage setting.
If you turn on Optimize [device] Storage, iCloud Photo Library will automatically manage the size of your library on your device, so you can make the most of your device's storage and access more photos than ever. All of your original, full-resolution photos and videos are stored in iCloud while device-size versions are kept on your device. You can download the original photos and videos over Wi-Fi or cellular when you need them.
I don't use iCloud Photo Library, so I'm not sure if there's a way to completely remove the photo from your device and keep it in iCloud.