Microphone and Audio Input are separate inputs.
I can see the confusion as they both use 3.5mm Jacks, however Audio Lines require a pre-amp prior to the output side, the pre-amp amps up the raw line to give it volume and this outputs digitally formatted data rather than Analog data.
The Microphone on your Android is supposed to be connected directly to a ...
Not possible without root but even with root SoX recording might not work.
Android Manifest Permissions
Android permission system has different Protection Levels (1, 2); Normal permissions are granted to any app without user interaction while Signature|Privileged (SignatureOrSystem) permissions (whitelisted in /etc/permissions/privapp-permissions-*.xml) ...
The only conceivable way I can think to achieve this would be the use of some kind of external USB DAC (digital-to-analogue converter), which involves routing the audio out through the USB C port
I've successfully done this using a cheap adapter-type "soundcard" (the 'Sabrent Aluminum USB External 3D Stereo Sound Adapter', bought on Amazon), which involved ...
The Cube ACR app is able to do this.
At the top of the menu of this application, turn "Enable recording" on. Then, when calling with whatsapp, you have a button to switch recording on and off. The recordings are then available within the app in AMR format (with the free version of the application), and can be exported, for instance to your google drive.