There are plenty of apps that will play FLAC and other hi-res files on an iPhone or Android. Some better than others (FWIW, my vote goes to the Onkyo app in terms of sound quality - and I have tried many, believe me - your mileage may vary).
However, I haven’t yet stumbled across a ‘similar enough to Roon’ mobile solution that will allow incorporation of metadata beyond album art. For me this is where the value of Roon hits the road. I’m meaning album notes, credits etc. Anyone have any success with this?
I have tried both Plex and Emby with this. Both do some things, but ultimately it’s disappointing. You can add free text in the album overviews section in Plex, so I experimented with adding web links in this space to Last fm and Music Brainz webpages, and also for the Qobuz web app page for the albums. Good idea, but the hyperlinks (though a different colour) didn’t work! Troubleshooting didn’t solve it, so I have posted on the Plex forums to see if this can be resolved. Also, Plex can’t - from my experience - sync files any greater than 320 Kbps to mobile devices, and transcodes hi-res files down accordingly. Bummer.
Then with Emby - again you can add whatever you like in the free text areas, and they already have custom links to metadata sites. However, the links and free text aren’t visible in the mobile apps. I did seek clarification in their forums, but it appears they removed the free text and links from their mobile apps for music libraries - apparently people were complaining that scrolling down past this was irritating - they just wanted to click immediately and listen! You can sync hi-res files in their original quality to mobile devices (whereas Plex couldn’t), but I found the end results disappointing. Perhaps to do with the quality of their player. To be fair, they aren’t catering for anal audiophiles.
I appreciate of course that with the mobile Tidal and Qobuz apps there is a certain amount of metadata, but it’s not the same (and in Qobuz’ case, it’s presented so unattractively it’s fairly off-putting, IMO).
I get too that you can of course just launch a web browser and search for as much metadata as you like while listening, but it’s not the same.
So, any experience of hi-res mobile apps (in my case, iOS) that can handle metadata? Of course, being able to access Roon remotely would obviate the need for all of this, but clearly this ain’t happening yet. I have read up on ZeroTier for use remotely with Roon, but the consensus seems to be it doesn’t play nice with iOS.