Actually, I have a spare android phone which is connected to my old speaker system. I wanted to connect to that phone via Bluetooth as if I'm connected to a Bluetooth speaker. So that, I can route audio to the speakers using any device connected to that spare phone (Indirectly giving the Bluetooth functionality to the old speaker system)
Edit: I saw the related questions, those questions needed any working method that solves it. I don't want to use any third-party app like a music player or anything. I just want the spare android phone to be connected as an audio source to my phone.
The first image is the screenshot of a Bluetooth headphone connected to my phone. I want the same settings as "Media Audio" when I'm connected to spare android phone.