Backing up contacts to iCloud!

iOS & iPadOS

Good day, I am using a IPHONE XR. With IOS 14.2. And, would like to know? How can I get my device to make a propper back up of my contacts to Icloud? I signed into my Apple account with my old 6Sand the contacts that it retrieved from Icloud were only about 50% of my actual contacts? I cannot work out what the problem might be. I will appreciate any advice!