This is the Alpha release of Phaser 3.
Please see the Phaser 3 Dev Logs from entry 91 and onwards for more details.
The phaser.js is a dev build, ideal for local testing and includes full source map data and comments (hence the huge file size).
phaser.min.js is a minified build, with no source map and comments stripped. You can use this if you'd like to upload a test somewhere and save some bandwidth. With gzip enabled it's just 104KB in size, including all Game Objects and both Canvas and WebGL renderers.