Stream sounds from a computer to a phone, e.g. to a BT speaker connected to the phone:
Install SimpleProtocolPlayer NG from F droid Configure with IP of your streaming PC, e.g. 10.0.0.XX, port 12345, set sampling to 48kHz
Using pulseaudio:
pactl load-module module-null-sink sink_name=streamtcp format=s16le channels=2 rate=48000
pactl load-module module-simple-protocol-tcp rate=48000 format=s16le channels=2 record=true source=streamtcp.monitor port=12345 listen=0.0.0.0
Redirect your apps to the NullSink using pavucontrol or any source control app for pulseaudio
Then click on the phone on play.