Calls in speaker mode only are for listening, no for speaking (One way conversation in hands free mode).
Launcher: Pixel Launcher
1.- Unlock the phone
2.- In the desktop, press the dialer app, (Google Dialer v14.0.175904292 in my case)
3.- Make a call
4.- Whith the call in progress, press the “Speaker” button to enter in hands free mode.
5.- Bug: You will ear the conversation, but your listener can not ear you.