A few months ago I've started my project using Colyseus and Phaser 3:
After hit a few walls and considering it was my first project it took me some time until I was able to get the physics working on the server to avoid cheating.
The way I get it done was using Phaser physics engine P2JS: https://github.com/schteppe/p2.js
Doing this I was able to avoid an overhead of modules and stuff required to run a headless Phaser.
Here I bring for you a small example of how to recreate a Tiledmap using P2JS:
I'm still finishing the dwdgame version 1.2.6 in which this demo will be fully integrated.
Hope you like it, and please I would love to get any feedback!