Cool theme interpretation. I liked the RPG integration and believe you could take it further. A few examples I have are:
1. adding an image to each colour indicating it's action. This way, the player doesn't have to rely on the introductory explanation to remember what each of the colour blocks do.
2. perhaps hitting the same colour blocks in a row would cause some sort of mega action of that colour. For example, hitting 3 red blocks in a row would do a mega fire attack.
Overall, great game! Check out my game if you get a chance, I used Phaser as well: https://itch.io/jam/game-off-2018/rate/338739