Use device as Bluetooth receiver I recently got a new phone and would like to use my old device as a bluetooth receiver for my stereo. I'd like for it to work like a bluetooth receiver such as this one. (Pairs as speaker and offers 3.5mm output) Being able to control playback (pause/play, backwards, forwards) would be a bonus, but not necessary.

Please note the device is running Android 2.3. (Yes, I know that's very old)
Quick answer: NO. Doing a quick Google search to confirm my assumption, it does not look like there is any (easy) way to use the phone as a Bluetooth receiver. One problem is that the device should disable the headphone jack when Bluetooth is connected.

I personally have old Android devices (phones and tablets) connected to pretty much every audio appliance in my house (like stereos and powered speakers) using either the headphone jack or Bluetooth (using the device as a transmitter with a separate receiver). I just use the actual connected device to play the audio. One option is to connect to the audio device normally and use an app where you can "remote control" one Android device with another.

Alternatively, it looks like you can stream from one Android device to another using Wi-Fi. An app like SoundSeeder on Google Play makes this possible.

Hope this helps!