Pixi is the rendering engine used by Phaser. More relevant is the different physics engine Phaser supports (Box2D, P2 and its own lightweight arcade physics engine). Also Phaser is Typescript but distributed as JS. You can link it directly with Typescript too though which is why I like it a lot.
Phaser.js was at some point in the past written in TypeScript, the current version is implemented in JS and you can use it from TS if you wish. (Also, they will probably ditch the Pixi renderer in the next Phaser version and use their own.)
