These are tutorials I found particularly useful.

Modular Game Worlds in Phaser 3 (Tilemaps #1) — offers a good foundation for understanding how levels (tilemaps) are created in video games. (Everything from Mario to Final Fantasy.) Additionally, this tutorial does well in explaining how to build tilemaps in Phaser. I suggest you stop when you reach the Moving with Physics section. That becomes a whole separate tutorial, specific to platform games.

Grid-Based Movement in a Top-Down 2D RPG With Phaser 3 — focuses on the classic grid-based movement seen in games like Final Fantasy and other jRPG games. You can either follow the tutorial, or explore the finished code in GitHub.

Making your first Phaser 3 game — if you want to start by making a Mario-style game, this tutorial offers a good foundation for using Phaser's physics engine, without overloading you with other topics (such as tilemaps) Though, if you aren't interested in making Mario-style games, you may want to find another tutorial to start with.