When I worked at Home Depot, people (customers) would be on calls on speaker all the damn time. It was annoying as hell. And they all seemed to be at max volume...like they all had a hearing problem. They were literally holding the phone up to their face while talking on it. What was so damn difficult about using it normally so everyone else couldn't hear the entire conversation.
There was one time someone was doing that, and something funny was said. A coworker and I heard it all and we both laughed. The person in the store stopped, looked at us, and said something like "Are y'all listening to my private conversation?" To which I said, "Yes...and so is everyone else. Maybe take it off speaker so we don't have to." They didn't like that. And I didn't care.
Using the speaker is for when you're driving or your hands are busy doing something else in a private setting. Earbuds are for when your hands are busy doing something else and you can't hold the phone and you're in a public setting. But if you can hold the phone, then it needs to be on normal so everybody else can't hear your "private" conversation.