Well, I had to try it…

@Nick_Craver I used to keep a USB-C adapter and USB Ethernet adapter in my go back for his exact reason.
And to test network connectivity without getting out a laptop, of course. 😂

I had a USB-C 10Gbit SFP+ adapter come across my desk. Of course plugging it into my phone was the first thing I did.
It was designed for Macs so idk if the drivers were extra weird but it didn't work. :/

@hmhackmaster On phones, FWIW I bet the power output is too low to support it - takes a bit of wattage to run those and I wouldn't be surprised if it's higher than needed. Consider the heat sink they have on 'em - that's how much power is running through to dissipate.
@Nick_Craver It was a powered box, so I don't think that was the issue.
It wasn't an Atto box (those are Thunderbolt) but it looked similar (just bigger). It was too long ago for me to remember the brand and can't find a picture.
Part me is slightly worried I am misremembering and it was a Thunderbolt thimg but I don't think I would have bothered to try it if that was the case...
@hmhackmaster Most I've seen have been Thunderbolt (because 10Gbps over USB-C is a rarer customer hit and the overhead of USB would yield complaints too)
@Nick_Craver when I pulled up picture of the Atto boxes I remembered more about the situation so you might be right.
This probably would have been around 2015/2016-ish (when I was working on adding a 10Gbit WAN link to the existing 2x1Gbit dedicated fiber lines) so whatever box I had was a pretty big and expensive box (I think the Atto boxes were $1700/each and we got 20 of them).