If it's set to pull USB power in Power Settings, the IQ4 will pull power off any suitable USBC power source it deems capable. Whether one can charge, or at least slow down the rate of discharge, with this depends on how much power your power source can push.
I've used Anker's and Hyper's USBC power banks to great effect. Since I shoot tethered, a HyperJuice 98Wh/100W external power bank plugged into a 2018 MBP, tethered to the IQ4, will power both for about 6 hours of tethered shooting before needing a battery change on the Phase and a juice-up of the power bank/laptop, although for whatever reason (cable voodoo, likely) the IQ4 sometimes doesn't start pulling power even when you tell it to. Using a short and heavy USBC-USBC cable, and connecting to USBC before starting the back up (and making sure that the 'heartbeat' charging LED starts showing) when tethered seems to help. That said, I usually open up the Power Settings panel before shooting just to make sure that I'm seeing a few watts of USB power coming in before shooting just to get around any rude surprises later in the shooting day.