With pinggy.io you can share your Memos instance from localhost with just a single command. Replace the port 5230 with the port where Memos is running.
Pinggy will give you a URL like https://ranlkfsbjkxry.a.pinggy.link. Use this URL to reach your notes from a phone or another machine.
Memos has its own sign-in, so the tunnel does not expose your notes to anyone who guesses the URL. Turning on Password Protect above adds a second gate in front of it.
For the full walkthrough, see self-hosting a note-taking app with Memos.