By Josh Morony
When building a game with Phaser you will likely have various objects on the screen. You might have the players character, a floor or some walls, some enemies, items, and so on.
These entities are going to need to interact with one another in some way to make the game playable. If a player touches a powerup then the powerup should be destroyed and the player should gain its effects, if the player hits an enemies bullet they should probably be hurt or killed, if a player jumps onto a platform they should land on the platform (not fall through it).