PhpStorm has a button that can automatically open your website in a web browser without setting up a server

Similar to Eclipse Mylyn: you can create tasks or retrieve them from your ticketing system, and each task keeps its own context (opened files, modifications, etc.).

PhpStorm is clearly being developed continually, which gives confidence that it will be available for some time and is not abandonware.

Save time of building your own or integrating libraries for testing RESTful Web Services. PHPStorm enables you to test endpoints without leaving your workspace or disrupting your workflow . You can code your endpoints in one window and test it immediately from another window.

Supports Twig and Laravel's Blade (among others). Technically the later is part of a framework which Phpstorm supports but I've seen IDEs (e.g. Netbeans) with Laravel support but no blade support so it does deserve a notable mention.

Quickly rename classes, methods, and variables used across multiple files in the project.

It recognizes Vagrantfile and allows full control from the IDE.

Type codes with pleasure. Delay of visual feedback on a computer display has an important effect on typist's behavior and satisfaction, as cited here.

Lots of plugins from JetBrains and the community are available, from useful things like support for Docker, Vagrant, Angular, Vue.js and more useless (but fun) like a nyan cat progress bar.

This allows execution of needed commands without switching to other windows. It also keeps track of what's happening right in the IDE, which is especially good with Vagrant, because you can connect to a VM in a single click.

Allows users to manage their repositories directly from the IDE with a GUI which lets you do all Git commands.

Active development work on plugins is always a plus, as it can extend the use of the IDE.

It allows monitoring code and sync the files that need to be changed with a remote server. This works more efficiently than libnotify and faster than vagrant auto rsync.

Phar support allows running complete applications out of .phar files.

The database tab, while not perfect, provides all the tools you need for daily usage. You always have your DB overview on the side (you can hide it when not needed).

Ability to setup custom external commands, which is something inherited from eclipse and found lacking on netbeans.

Has built in support for Xdebug including remote debugging.

Not just for PHP, HTML and JavaScript, but especially good is SQL inspection and auto-completion of tables and fields. You can see at a glance, that your DB structure is in sync with your code.

PHPDoc is a documentation generator. It allows automatically generating documentation from specifically formatted comments.

Supports Symfony2 (including Twig and Doctrine), Yii frameworks, and Laravel.

PhpStorm has two types of autocompletion: structural completion and word expansion.

Structural autocompletion makes predictions based on its understanding of PHP, while the latter tries to predict the word currently being typed based on previously typed words. Word expansion also works in comments and docstrings and it's similar to vim's omnicompletion.

Both types of autocompletion work extremely well, have little to no problems and are quite fast even when loading suggestions on the go.