Volumio Version:2.779
Hardware: rpi4
DAC:onboard
HI,
I want to have this setup 
Connect iPhone through rpi4 USB and then listen music through rpi4 jack output or via other USB connected to a dac? This is possible through volumio?
Thanks.
Do you mean USB tether your phone to the RPi to enable internet access for the RPi4? If so it is theoretically possible, but it would mean you altering the networking set by Volumio, and you may well have problems (ie. do so at your own risk). I had a quick search of the forum, and I came across one person doing something similar a year ago.
You can listen to music from your RPi4 jack output or an external USB DAC, but no idea if the latter would interfere with your USB tether.
Hi,
To go on a location where I have only 4g internet access to my phone, connect it to rpi4 via USB then listen spotify from iPhone to rpi4 jack output…
Thanks
It isn’t at all clear what you are asking.
You can cast the Spotify from your phone to the Volumio.
Or you can get a Spotify plug-in for Volumio so you don’t need to cast from another device.
You can use the Wi-Fi hotspot of your phone as the internet connection for Volumio.