I think this is probably a spam or solicitation call and probably not a collection call, although I'm not sure. The call came in, rang twice, and stopped. My cell phone company labeled it as "suspected spam" (which happens with sales and collections calls), but collectors usually let it ring the entire 4+ times and go to voicemail if unanswered, whereas sales rings enough to allow an answer but not go to voicemail.
I think it could be a bath remodeling company because we recently entered a contest and are possibly interested in their work. We asked for no calls and email-only contact initially, but the phone immediately started ringing within an hour of that registration and hasn't stopped. We won't answer now.