"Enable" is indeed the key word. VoLTE does support AMR wideband, and there are other wideband codec evolutions in the pipe. But it also supports AMR narrowband

"Enable" is indeed the key word. VoLTE does support AMR wideband, and there are other wideband codec evolutions in the pipe. But it also supports AMR narrowband. So it'll be up to the operator to decide between higher voice quality or higher capacity. That will depend on how much spectrum is available, and load. It may even change during the day depending on a cell load.