This is another new official tutorial from the Phaser and Facebook teams: "In this tutorial we're going to learn how to create and use Leaderboards with the Facebook Instant Games Plugin for Phaser 3. Leaderboards are a free hosted service that Facebook provide, which allow you to easily set-up and create a leaderboard for your game.
A leaderboard is, as the name implies, a score board. Where players vie for a better ranking. You have some basic controls over the format of the leaderboard data, the sort order and the format of the score. You can also opt to create a leaderboard that is context specific, or global.
This tutorial will cover how to create, populate and display leaderboard data in your game."