This zero-build game needs the vendored Phaser library, which isn't bundled in the repo.
To fix (one-time, needs internet once):
1. Download phaser.min.js (Phaser 3 latest stable, ~1.2 MB) from
https://cdn.jsdelivr.net/npm/phaser@3/dist/phaser.min.js
2. Drop it at v3/assets/vendor/phaser.min.js
3. Reopen this index.html. Nothing else needs the network, ever.