It can be rude to the business, and to who is on the other end of your call. It can also be neither if you use common sense. Information security is the same, use common sense.

Dont hijack a spot in a cafe all day. Keep it moving after a little while. These places have very limited seating. Never take important calls in public if you cannot control your environment. If you have a loud ass speaking voice, being on a work call is as bad as someone facetiming with speakerphone on. Common sense defeats all of these issues.

Source: remote worker of 4+ yrs