How do I input a CSV of Contacts into iCloud

icloud.com only supports importing contacts from a vCard file (.vcf). Try exporting your contacts from Outlook as a vCard.

You can learn more here: Import, export, or print contacts on iCloud.com - Apple Support

If you own a Mac, the following support article can help you import contacts to the Contacts app from a CSV file, which you can then sync to iCloud: Import contacts into Contacts on Mac - Apple Support

You have the option to transform your CSV contact list into VCF format, which is compatible with iCloud. I've come across a recommended converter tool with a manual that can assist you in this process that How to upload contacts to iCloud. Once you've successfully converted your contacts to VCF, you can proceed to upload them to your iCloud account.

Also check: Import, export, or print contacts on iCloud.com - Apple Support