On Windows x64, the remote debugger listens on an additional port to allow debugging 32-bit processes running under the WOW64 ...

On Windows x64, the remote debugger listens on an additional port to allow debugging 32-bit processes
                running under the WOW64 (Windows 32-bit On Windows 64-bit) emulation layer. The /wow64port option
                allows this port number to be configured. This may be useful to accommodate a hardware firewall. 
                If unspecified, the debugger will attempt to use 4019, but will fall back to any unused port if 4019 
                is already in use.
                

Note that it is not recommended to ask Visual Studio to directly connect to this port, as this will only allow for debugging 32-bit process. Instead, if Visual Studio connects to the primary port (see /port), it will automatically switch to the 32-bit port when needed.