Cloudflare's abuse form will not let you submit the report if you don't include a URL that currently points to their network. There're no options for phishing / scam domains for which they're the registrar and/or DNS hosting.
Failing that:
> If Cloudflare is listed as the registrar on an ICANN WHOIS listing, you also can email reports related to our registrar services to registrar-abuse@cloudflare.com