What version of Android does your phone have? Does it have USB OTG? If so, was it included with the OS or did you have to install it yourself? And what kind of connection (USB cable and/or adapter) are you using?
The cable I use is just an ordinary USB OTG cheap adapter.
My phone is this one
https://www.gsmarena.com/samsung_galaxy_alpha-6573.phpIt has USB OTG by default and android 5 lolipop, but it seems that it can only send sound to the keyboard and can't receive, as I tried the default recorder and the one that AnupamEnosh mentioned before and noone worked.
On the contrary, the tablet works great with both apps and it produce very clear quality sound, especially with the Anupam's app. My tablet is this one
https://www.gsmarena.com/lenovo_tab_2_a10_70-7089.php It has android 6 marsmallow and USB OTG support by default.
From a quick search that I did, I found that my tablet has some extra settings at the developer options menu, so you can choose what the usb will do, but at my phone I don't have these, so maybe it is a benefit of android version 6 (see screenshots).
Dear Anupam, thanks for this link, this app seems a gem! Now I don't need to convert to mp3 in order to send a song via social media. You just choose "High" setting at the "quality" menu and you have a nice MPEG-2 AAC file at 44Khz, 16bit, 256Kbps stereo, that doesn't take much space. If you need the best quality, you choose the "superior" setting and then it makes a .WAV file at 44Khz, 16bit, 1411Kbps stereo.
What it would be nice to do now, is to find a way to play a song from tablet, by sending this via audio output to keyboard's audio input and recording at the same time from USB, but it seems android doesn't leave me to do this for now.. I can connect of course my phone to play the song, but I would prefer to do it all from the tablet.
Here I recorded some new samples of both formats:
https://www.dropbox.com/sh/i67w7e5jzmew5m3/AABz_rXEyR7VQSXVLw1BYf2la?dl=0[attachment deleted by admin]