This can get messy. You need to make sure that you’re using the right “thing”. If you are using a passive adapter or headphones, your phone needs to support audio accessory mode and many don’t. The mess is because most dongles, adapters, and headphones aren’t labeled with how they are built and we don’t know if they are active or passive.
The Pixel 2 has an onboard DAC embedded in its Qualcomm Snapdragon 835 SoC, but audio accessory mode isn’t supported. That means you need a pair of active headphones or an active adapter, like the dongle that came with the phone. The HTC U11 and Essential Phone are the same, but Motorola makes phones that do support passive headphones through the USB port. All phones should support an active adapter or headphones, though.
One more thing: Not all active USB audio products will work with all phones because manufacturers are able to use several new wires in the USB-C connection for extra features, like HTC did with the U11’s earbuds to provide active noise cancellation.
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