PHP is as general-purpose scripting language geared towards web development and often used in those contexts. Nevertheless it is not common known that the licensing behind the software is more out of a problem and making it more than only a lightweight issue packaging this for a free and libre operating-system.

Starting in the year 2000, the PHP authors have decided to remove the option to use PHP under the General Public License, so with beginning from PHP version 4. This left users with only the PHP License as an option, which is non-copyleft, but includes extra restrictions beyond most non-copyleft FOSS licenses.

 [...]

  3. The name "PHP" must not be used to endorse or promote products
     derived from this software without prior written permission. For
     written permission, please contact group@php.net.
     
  4. Products derived from this software may not be called "PHP", nor
     may "PHP" appear in their name, without prior written permission
     from group@php.net.  You may indicate that your software works in
     conjunction with PHP by saying "Foo for PHP" instead of calling
     it "PHP Foo" or "phpfoo"
     
   5. The PHP Group may publish revised and/or new versions of the
     license from time to time. Each version will be given a
     distinguishing version number.
     Once covered code has been published under a particular version
     of the license, you may always continue to use it under the terms
     of that version. You may also choose to use such covered code
     under the terms of any subsequent version of the license
     published by the PHP Group. No one other than the PHP Group has
     the right to modify the terms applicable to covered code created
     under this License.

 [...]
 

(Source: PHP 3.01 License)

Those restrictions specifically related to use of the PHP name. Ultimately, such licensing makes extra work for distributions and operating-systems and creates uncertainty for people wishing to modify PHP - as they navigate a license used nowhere else that awkwardly pulls in a trademark policy as part of it.

In the whole outcome and as result PHP violates the freedom to redistribute without “explicit” approval.