I seem unable to back up my contacts data, although I have tried to ensure everything is set correctly. My icloud contains a lot of the contacts,but many are missing...any suggestions please

RAWSki59, 

When you add a contact to the Contacts app, it syncs with whichever account is set as default in Settings > Contacts > Default account. If that is your iCloud account, it will sync with iCloud, if that is your Gmail account then it will sync with Gmail. 

Additionally, if a contact was originally syncing with Gmail it will remain syncing with that account unless you move it or also create one that syncs with iCloud. You may be able to export your contacts from Gmail and import them to iCloud though. Here’s how to import a vCard to Contacts on the iCloud website - Import or export a vCard in Contacts on iCloud.com 

Import a vCard

If the vCard contains contact information for more than one person, each contact becomes a separate entry.

1. In Contacts on iCloud.com, click the gear icon in the sidebar, then choose Import vCard.

2. Select a vCard to import.

Contacts from imported vCards are added to the All Contacts group. You can add contacts to any other group by dragging them. See Create and manage groups of contacts on iCloud.com.

Thanks. 

Hello RAWSki59,

Are you trying to restore an iCloud backup onto another device? If so, be sure to note that if iCloud Contacts is enabled then the contacts won't be duplicated within an iCloud backup, as seen here: What does iCloud back up? - Apple Support

Be sure to also check and see if there are contacts being synced from other accounts (such as a Google or Exchange account for example). This page can help with locating that in Settings > Contacts > Accounts: Use other contact accounts on iPhone - Apple Support

Cheers.