You shouldn't use speakerphone in public because it's rude.
David needs to talk to his doctor about his test results.
David wants to call the doctor's office.
David waits until he gets home and calls the doctor's office.
David puts his phone on speakerphone when he is on the bus.
David finds out about the results in the privacy of his home.
The passengers are annoyed with David and the bus driver kicks him off the bus.