how-to-play-hi-res-music-your-iphone-0
This means the music from your CDs ripped to B2, which will be Flac, will not be playable via the Music app on your iPhone.
That being said, the process to actually transfer music files from your B2 to your computer is quite straightforward. I have a wi-fi connected iMac rather than a NAS and Windows PC, so I use a Fat32 formatted USB drive connected to the USB-C port of the B2. You can do this also, or others can guide you in how to do this via your NAS setup.
From the B2 web-ui on your pc select the music album or track you wish to transfer and click on the 3 dots to the right hand end of the line. Select 'Add to Playlist'. This then appears in the playlist box on the bottom left side of the UI. When you've added the music to be transferred to your chosen playlist go to the B2 front panel and select 'Export Playlist' from the Playlist Menu. Use the rotating knob to select the playlist. This writes to playlist contents to the USB drive. Once complete you can then transfer the USB drive to your PC for subsequent processing.
I use the Import file option on Apple Music on my iMac to handle the transfer of music via wi-fi to my iPhone from here on, but others will need to guide you on what you do with Windows these days.
Hope this helps a bit.
Rob