All generations below mine...
...abhor actual phone calls and send voice messages through Whatsapp instead.
Which kinda makes sense, because actual phone calls are charged by the second, take longer to negotiate and are prone to failure, while compressed audio through whatsapp media is charged by the kilobyte in their data plan, is time-delayed instead of simply failing to transmit, and the net result is actually cheaper. Plus, the interlopers can repeat the messages to their hearts content, and those messages can be checked, before sending, for clarity.
Here is the jump to the topic: the messages are recorded using those 90 degree angles so they can see the screen at the same time they are recording, just in case the other party decides to send an emoji or (gasp!) text at the precise moment they are recording.
And during playback, they turn the volume of the phone down, in order to attain some privacy, and again hold the phone at that odd angle so they can hear the media like it was an actual phone conversation, but not being bothered by actual headphones, bluetooth or otherwise, while keeping the hand position to resume typing, or access once again the record button, at record speeds, no pun intended.
1 hour lost in my commute, observing 5 people doing those actions at the same time, in the metro, allowed this observation.