OP says: "A cursory investigation showed that Namecheap is providing both registrar and hosting services for this phishing site." So he already contacted the host, Namecheap.
I missed that. Well then... some other options might be gather evidence and upload to IC3 [1] understanding they may be understaffed or alternately discuss it on 4chan of whom I will not link. CC email the people at Namecheap when conversing with IC3.
Thank you for the advice. I'm not a citizen of the US so I'm not sure if me contacting IC3 would be appropriate. I'll probably reach out to them in a couple of days if the phishing site remains up.
[1] - https://www.ic3.gov/