Here are a few of the many reasons that PHP has become the highest rated tool in Web Development:
It has excellent performance and flexibility.
PHP Is well structured. Long chunks of code can be broken up into functions or methods that achieve tasks with simple code and are broken up into units.
Coding is consistent by simply making sure all of your code is indented in the same way, consistency makes your code easier for others to read.
If you know what you are doing you can write code that works by adapting to its environment.
Security is in the hands of the developer. A coder with a deep understanding of potential security holes might use Cross-Site Scripting (XSS), Cross-Site Request Forgeries (CSRF), code injection vulnerabilities, or character encoding loopholes.
It is very easy to make changes to any include. For example changing a phone number on a header can make the change for any number of pages that are included in your web design.
For these reasons there is no doubt that PHP has become the highest rated tool in Web Development.