Streaming with Bluetooth is really easy... Go to settings on your phone. Open the Bluetooth section. Turn on Bluetooth and start a scan.
The network music player will show up there as the Bluetooth device Player. Click on Player, pair and within seconds your phone will be connected to the player. Start an app, start playing and it starts streaming. Below is an example of pairing and connecting:
The Network Music Player supports Bluetooth 5.0 and that version is supported by most modern phones. With this version comes a wider range and increased transfer capacity which improves sound quality up to be like CDs. Bluetooth is backwards compatible, so you can use older devices, but they might not always be able to benefit of these latest features.
You can only stream your apps with Bluetooth, if you would like to do some settings of the Network Music Player itself (like set the default volume*) or do USB playback you have to use your home Wi-Fi network.
*The default volume level of the Network Music Player is initially set to 100% - that is appropriate for streaming since you want to adjust the volume from your apps in that case, but when you do USB playback (play tracks from the attached USB stick) be sure to lower the volume first.