How backup iCloud Photos if macOS internal drive is too small?

I have a 256GB iMac. And around 200GB of photos in iCloud. Therefore, my [Photos.app](http://Photos.app) is set for optimize storage. I have more space on my iPhone, so that one keeps all photos locally. What are my options to actually backup my photos? \* If I backup my iPhone to my computer, are the photos also in the backup? \* I heard you can make the Photo library be in an external drive, but that sounds very cumbersome since most of the time I don't want to keep an external drive connected \* I heard you can download everything you have in iCloud from [iCloud.com](http://iCloud.com), would that work to backup all the photos? Basically downloading all that periodically to an external drive \* Any other way? I like having all my photos on a server like iCloud, but I also understand that iCloud is a synchronization service, not necessarily a backup service.