iCloud Photo Library and storage usage on devices
It is not a lightweight version it's more like a preview and then when you're connected to the internet you have access to the photo in full resolution. Your iPhone will let some space to the photos it will just optimise the storage, not all photos will be in the cloud. But I'm not sure if it can handle 200Gb but some space in your iPhone will be used depending on how frequently you access your photos in the cloud.