Good enough for a garage system I guess. One issue is that at some point the phone will be so old that the O/S won’t support your streaming services apps, but by then you probably would have upgraded to something else.
I tried this initially when I was learning about all this streamer/DAC mess 5 years ago and yeah, it works (an Android phone). I put it on equal footing with USB coming out "raw" from a Raspberry Pi. But some cheap easy to use options available today like a $79 WiiM Mini that you can remotely control come to mind.
Many people trade in their old phones for a modest store credit when upgrading. If that "credit" is more than $80, I’d trade in the phone and buy a WiiM. Otherwise, repurposing an old phone instead of throwing it in the landfill is good.
It does have me wondering how using an old iPAD to USB adapter to DAC compares to say a WiiM Pro to the same external DAC. With the iPAD I can have a nice album art display I can see across the room.
Old phones as streaming sources
I'm curious how many of you have converted old phones to streamers. I have found that when I remove the sim card and shut off blue tooth and wire the phone to a dac with an appropriate USB adapter cable, my old iphone 6s makes a pretty good streamer. Just wondering what others experiance has been. It is a really economical way to source digital to a 2nd or 3rd system. You can even cut electronic noise further by running on battery power when listening and shutting off the screen once the music is rolling. Going one step further would be to transfer local files to the phones memory and turn off wireless altogether. I have not done this but theoretically it should help. I usually just run the Qobuz app and stream from that to my Chord Mojo. What's your experiance?