Hi and Welcome. My Name is ***** ***** I look forward to assisting you today with your question.
Yes, they will deleted from iCloud unless they are downloaded to another device. iCloud backup service is only to backup the entire iPhone and not just photos. The photos you see on iCloud are for sharing purpose mainly. The backup made on iCloud can be only retrieved after erasing the iPhone which you probably don't want to do.
You have two options in here. Either you backup them to your computer which is the best option or you can backup them to other online services like Dropbox --> http://www.dropbox.com/
You can download Dropbox from App Store. Dropbox is the best online service out there that you can backup with trust. After backing up to dropbox, you can safely delete them from your iPhone. The backed up pictures (on Dropbox) can be viewed online or can be retrieved back to your iPhone at any time you want.
Another alternatives for Dropbox are Google Drive or Microsoft OneDrive which can be downloaded from App Store.
If you have any questions or would like any additional information, please don't hesitate to ask.
Remember, this is not my final answer. If my solutions didn't work please don't rate me bad or poor. Instead please reply back to me and I will continue to help you until we fix the problem or you are satisfied.