Correct way to access local site on local network with my phone?

Correct, to reiterate:

When Sage’s development process is running, there is no dist/styles directory. Webpack builds and injects the styles on the fly using HMR. This way the browser doesn’t need to do a full reload, which is escepcially helpful for JS since it retains its state.

I have a little bit more in-depth explanation of how this process works here: