The adapter required to plug headphones into a smartphone that has eliminated the traditional analog 3.5mm socket.  Such devices only have a USB Type-C socket for a wired connection to a charger or external device.  The problem is that not all USB-C ports in a phone support analog output.  See 
analog audio, 
mini-phone connector and 
USB Type-C.
Not All Adapters Work
USB-C Audio can be analog or digital.  Because earbuds have traditionally been passive analog devices (no conversion), the USB-C port must output an analog signal.  The only true way to tell is to try it (like most everything in the tech world).