I used one of the temp mail addresses. No phone number (or any other verifiable) information required.
Even then, I don’t know if this is really a huge problem given the nature of this tool.
This looks like a really cool little CLI script, and I could see myself using it as a regular CLI tool instead of whois and Googling. It looks really good, it gathers a lot of extra info, and uses a bunch of highly regarded external sources like virustotal, shodan, graynoise and more.