According to a new report from Netcraft, the current adoption of PHP as of January 2013 on the web has climbed to an astonishing 244 million websites. Netcraft tracks the evolution and deployment of programming languages since 1995 with it's Web Server Survey.
Basically PHP makes up about 40 percent of the 630 million total websites on the Internet today.
Many of the world's most popular content management systems use PHP for their underlying architecture and logic. CMS's such as Wordpress, Joomla, Drupal all are built on PHP. There are no signs that it's dominance will halted in the near future.
SOURCE: https://news.netcraft.com/archives/2013/01/31/php-just-grows-grows.html