haveibeenpwned.com does not use the k-anonymity method that you've described when searching for phone numbers: https://www.troyhunt.com/the-facebook-phone-numbers-are-now-...
Still, if I had to chose between hibf.com and hibp.com, I'd lean to hibp.com since Troy is a known name in the industry and has offered this service for a long time without any complaints.