How to delete all phone numbers in my iCloud

Hello, rofiat112.

To delete the phone numbers in iCloud, you must disable Contact syncing in iCloud. You'll have to do this on any device that you don't want having access to those numbers and contact info.

If you only want that info to be on you iPhone, then disable Contact syncing on all of your devices.

Set up and use iCloud Contacts - Apple Support

I ope the explanation above answers your question. In effect, iCloud mirrors what you have on your devices when it is active.