What you need to do is clone the Phaser sources into your project's "www/js/libs" folder. Then wait a bit for background scanning to complete, which is when the parsing is set up.
And then you can use code completion, as shown in the screenshot above (click to enlarge it). Another approach is to create a symlink to your project from the cloned Phaser sources. Yet another approach is to use a PHP project, instead of an HTML5 project, since the PHP project has an include path setting in the Project Properties dialog, where external sources can be included for editor purposes, where the "phaser/src" folder can be registered.
The approach of using the Phaser sources actually conforms to the standard way of developing applications with Phaser, as stated here: "You should include phaser.min.js in your html when you deploy the final, finished version of your game. Until that point you should use phaser.js (the non-minified version) as you'll get accurate debugging / line numbers from it should something die internally." (See here.)