Refrain from using Namecheap as their registrar for the bitwarden.eu domain, as Namecheap is not very strict about policing malicious users of their services. Notably, the bitwarden.pw domain is also registered via Namecheap.
Refrain from using registrar “privacy” services that hide the registrant identity. Not surprisingly, the bitwarden.pw domain also hides the identity of the domain registrant.
By clearly identifying Bitwarden (or 8bit Solutions LLC) as the owner of a domain, and by using only reputable registrars, it would be a lot easier for users to spot phishing sites.