saving photos in icloud

muggy is right. Even when you are making regular iCloud backups of your iPhone you will not have a backup of your photos, if you are using iCloud Photos as well. Your iCloud backup will only include data that are not already stored in iCloud by an app, for example Photos or Mail.

See this user tip for some background information: Three Good Reasons for Using iCloud Photos Library and when not to use it - Apple Community

I really like iCloud Photos to store my photos, for several reasons. When we are using iCloud to store the documents and data of an app, we will get an off-site storage of our data. All our devices can access them there, and any changes will be updated across all your devices. When one of our device is lost or stolen or damaged, we can recover our documents and data from iCloud. This is a partial backup. But iCloud does not keep a long-term history of the changes you make, like Time Machine does. When you make a mistake and delete something importing and do not notice it immediately, before the deleted item is gone from recently Deleted, you cannot recover it from iCloud. Or if you accidentally select more than one photo, when you change keywords or titles, you can mess up all your selected photos at once. We need a separate backup to protect us from user mistakes, unless we are perfect. A backup cannot be the files we are using and working with. A backup needs to be a separate copy, that is never touched.

There is a way to use iCloud as a backup, but it requires a lot of work. I am using my 2TB iCloud storage plan and iCloud Drive to back up the original image files I have recently imported, until I connect my archive drive to store the photos there. we can use iCloud Drive as a backup and store copies of important documents and data, as long as we do never touch the backup there unless we need it to recover something. The one thing we cannot backup to iCloud Drive is a Photos Library. The syncing will damage it. If we want to store a safety copy of a Photos Library in iCloud Drive we can only store it there, if we keep it in a separate folder and compress the folder, then move the zipped folder to iCloud Drive.And the item has to be small. There is a size limit for items on iCloud Drive. And we cannot use the backed-up copy of the library directly on iCloud Drive. We have to copy it to a local folder and uncompressed it there.

Macs do not back up to iCloud. For that you would likely use an external drive and Time Machine (or equivalent).

You can back up your phone to iCloud. How to back up your iPhone, iPad, and iPod touch - Apple Support

iCloud also serves as a synchronization service so that you can sync files, photos, contacts, etc. across your devices. See iCloud - Official Apple Support