Free Texture Packer is an open source tool that allows you to pack multiple images into one atlas for you games or sites. It's compatible with Phaser 2 and can be used to pack and trim sprite sheets.
It also includes features such as detecting identical sprites and optimizing images. For Phaser 2, simply drag and drop the sprites into Free Texture Packer and export them in JSON (hash) format.
The output will be two files (one packed .PNG, and one .JSON) that you can then load using load.atlasJSONHash in the preload function of your Phaser game.