The technology is that the USB is a digital format and the headphones 3.5mm is analogue..so there must be a DAC in between. As I said the Apple 9.99 one has extremely good performance figures. You have not identified the phone you are using which obviously if it as Apple iPhone is designed for this adaptor. On Android phones, the volume is restricted,..but there are workarounds.. These usually require the purchase of the USB Audio Pro software. There might be some odd limitation on your phone.
For my part , I have had plenty of success with Android phones and Cyrus soundkey, and the Apple adaptor ..the Cyrus is much better...but at 8 times the price!.