I’m not 100% sure what you’re asking. Do you want to have your FLAC files on your phone or do you want to be able to access them remotely? Neutron Player is a good app that has tons of flexibility and can playback your FLAC files.

Also, restricting to streaming? Do you currently not have a streaming service (Spotify, Tidal, Amazon Music)? If not then Apple Music offer Hi-Res Lossless (and Dolby Atmos if you have the capable device) or you can use Qobuz as it offers a lot of Hi-Res/Lossless music. You have a lot of choices.

I have exclusively used iPhones my entire life. I don’t know what you mean by “restricting to a streaming service”, you can play FLACs on iPhone with a 3rd party app just fine. Just be sure to get one with enough storage for your library.

VLC can handle FLAC files I use it sometimes.

Here’s the scoop on audio file resolution on Apple Music.

I use an iPhone 11 Pro and Apple Music. Almost everything (>95% of my download music) is available lossless (44.1k 16bit) and some (20%?) is available in high-res (anything higher than 44.1/16, hi-res file type is ALAC)) . By default Apple Music configured to stream and download lossy, but you can select either lossless or high-res for each independently. All that applies to music on the phone.

Getting the file to a DAC: 1) using Bluetooth everything down samples to lossy, 2) using Airplay 2 everything down samples to 44.1/16, 3) tethered using USB everything plays at the highest resolution on the phone I’ve seen files play at 44.1/16, 48/16, 96/16, 96/24.

I haven’t used other music services, so I can’t help with them.

I use Plexamp to serve my files to my phone. It’s works great and they have a client for basically anyone.

I’m on iPhone. I have been for years now.

I use Spotify for music discovery, and most of my “offline sync” music, because it is relatively okay quality, but allows me to save thousands of songs without having to worry about storage.

For when I’m on WiFi or want to enjoy something higher quality, I have a Jellyfin server with my FLAC collection. Some of the albums / artist on there, I have downloaded or “synced” to my iPhone using the app Fintunes. This way I can enjoy my favourite tunes in the highest quality, without needing or wasting my LTE traffic.

Overall- my iOS listening experienced is bottlenecked by the Bluetooth devices I listen to the music on. I can still tell a difference between 320k MP3 and FLAC, but it’s definitely not lossless. I definitely prefer listening on devices that support AptX or LDAC.

Hope this helps!