This post shows steps to Play Songs from mobile and listen on laptop/desktop speaker over Bluetooth. The steps are performed on Ubuntu 16.04, there might be some issues for later Ubuntu version, you can try.
Create a file as below,
vim /etc/bluetooth/audio.conf
# This section contains options which are not specific to any
# particular interface
[General]
Enable=Source,Sink,Headset,Gateway,Control,Media
Disable=Socket
Install Blueman as,
sudo apt-get install blueman
$ sudo apt-get install pulseaudio-module-bluetooth
Start blueman manager as,
$ blueman-manager
You may see a window like below,
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Start Bluetooth on your mobile and make it discoverable, now click “Search” icon in blueman-manager window, so you can see your mobile gets listed in blueman manager like below,
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Click “Setup” and “Pair Devices” and Next, once the device is paired successfully, click “Connect”
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Once the mobile is paired successfully to your laptop, just play songs on mobile and you should be able to listen those on your laptop.