You are gapped twice.

Any lossy codec discard out information.

If your source is lossy like Spotify, you will have some generation loss due to its lossy codec.

If you use Bluetooth, again you are using a lossy codec. In case of PX7 and iOS, the only common codec is the mandatory SBC.

Sounds like a disaster. However, what you can do is take a couple of lossless files (ALAC as Apple don't like FLAC) and load them on your phone. Also transcode them to e.g. 256 AAC.

Do a listening test (preferably unsighted). Can you really tel the lossless and the lossy sources apart over Bluetooth? Would be surprised.