There are a lot of IDEs for Php developer such as phpStorm, Netbeans, phpDesigner, etc. In my humble opinion, Eclipse and PDT plugin is still a good choice for some reason:
  1. Cross Platform:  it can run every where  as long as your computer have been installed Java before.
  2. Multi language support: Eclipse now is not IDE, it's become an IDE platform (I think), you just need Eclipse, search sufficient plugin, it can support a lot of programming language ( We also have Pydev for Python)
  3. Extendable: a lot of plugins for eclipse. If not, you can dev by your self by following official guide. 
For PHP , Eclipse does not provide package solution like java, C/C++ or Xml. We need to install PDT plugin to have PHP perspective. So, the installation process will be in 2 steps.

 1. Step1 : Run Eclipse standard package:

 - You can download Eclipse standard package at  official download page. Be careful of OS version ( Linux, Windows, MacOs and 32bits vs 64bits).

- Download and upack source code. Find excutable file to run eclipse at the first time:
Eclipse excutable file in Windows and Linux(Ubuntu)
- Run Eclipse to config default workspace ( project's source code location).
Can check into "Use this as the default and do not ask again" option
  You can see that, Eclipse standard package have java perspective in default.
Now, Let's install PDT plugin to get PHP perspective.

2. Step 2: Install PDT plugin

Go to PDT official plugin homepage an get the current Update site link.

At the time of writing, PDT plugin version 3.2  is released .
Copy that link, and open tab Install new software in Help menu.
You will see Install windows like the following.

Place the copied link into Work with text field, and click add button. You will see : Add repository dialog like the image below:

add the repository name ( whatever you want) , click OK. You will see the confirm dialog.
Choose PHP development tools, and follow the instruction of plugin installation screen.