Bluetooth connections to a DAC can be lossless for high-quality, CD-specs bitrates, but some additional steps are necessary.
First, pair the phone with the DAC using Bluetooth.
Check the properties of the Bluetooth connection with the DAC, make sure that the Codec in use is LDAC
In the Settings of the phone, access Developer options at the bottom of the list
Inside Developer options, go to the section about Bluetooth audio, and select Bluetooth audio LDAC codec: Playback quality (by default it is Best effort (adaptive bit rate), and that means having a sub-optimal connection speed). How far is Best effort (adaptive bit rate) from optimal quality depends on your mobile, as it might pick any value from high-quality 990kbps to low-quality 330kbps, so manual override is often necessary to get the high performing setting.
Pick Optimised for Audio Quality (990kbps/909kbps), this bandwidth is sufficient to stream lossless audio data at 44.1 kHz / 16 bit. This article https://www.soundguys.com/ldac-ultimate-bluetooth-guide-20026/ on SoundGuys.com clearly shows how the Playback Quality impacts the frequency response of the connection, with the lowest setting, Optimised for Connection Quality, filtering at 18 KHz:
If both 660kbps and 990kbps are fully covering the frequency range of CD audio (22.1 KHz), why bothering with 990kbps and just stick with 660kbps? The noise floor of the 660kbps connection reaches -74dB at around 15kHz, while the 990kbps connection remains comfortably below the -96dB mark:
After returning to the previous menu, the quality settings for Bluetooth have been set for max audio quality. Please consider that the distance between the phone and the DAC should be as short as possible, and with no obstructions to the connection, to minimize the risk of drops during playback. Should continuous drops happen, set the Bluetooth audio sample rate to 44.1 kHz and Bluetooth Audio Bits per Sample to 16 bits/sample.