Optical all the way if you can.
Don’t know how you could do this mobile with out a dap or something like a W2 with usbc input and optical output.
Still a usbc from a phone to Mojo is hardly crap for mobile use is it?
Still way way better than Bluetooth.
spdif coax is also fine I find.
In office I'm using it with M2teach hiface 2 usb > spdif dongle which is my long trusted friend - makes things musical and more organic, it's an excellent portable decrapifier and highly recommended if you can find it second hand as it's not produced anymore - I also find using it with batter power (you need single usb female to dual make cable) there's further improvements to be had.. I just use it out of my iPad at work to keep things simple.
At home, I have ifi iusb micro with ifi ipower x > m2tech hiface 2 > additional ifi spdif decrapifier with 5v ipower > optical out > Mojo 2. I also use Mojo 2 with clean power from the iusb in desktop mode. It's has a lovely delicate, organic, wide and warm sound - in one word, magical.
I also have ifi streamer, which is probably comparable if a little worse. I find the little ifi spdif 2 dongle decrapifier is quite nice to uplift whatever source you have.
I'm now looking at getting Xduoo x10 II usb > optical converter as I need something portable with optical out for work.. but I'm not sure if it's good enough, I have no idea if it does reclocking and the quality of it's components.
I'm a huge decrapification fan as you can see. Once upon a time IFI was legendary with their stackable decrapificators. from USB to SPDIF, I don't know why they've given up on that segment over last couple of years and just doing dacs/amps.
* Some DACs don't need decrapifiers - my Apogee Element doesn't care what I plug into it, it does it's own sanitisation to such a high standard it always sounds fantastic. RME ADI 2 seems to benefit a little bit. Mojo 1/2 really needs it