If you have important photos you should have multiple independent backups. First, as muguy noted iCloud is NOT an archiving service, it is a syncing service, so it is useful for transferring photos to other devices such as a Mac, iPad or Windows PC if you have iCloud for Windows. Once the photos are on another device you can export them to folders on your computer drive.
There are several excellent archiving services that work with iOS devices: Google Photos, Dropbox, box.com, Shutterfly, Amazon Photos, Microsoft OneDrive, Livedrive and others. Some also offer sharing and organizing features, including Google Photos and Shutterfly.
I sync photos to iCloud, but also export them to the Pictures folder on my Mac, where I also store photos taken with my other cameras. Google Photos picks up all of those as well as my iPhone photos. I also back up photos to Livedrive and Dropbox.