The biggest advantage of PHP over Perl is that PHP was designed for scripting for the web where Perl was designed to do a lot more and can because of this get very complicated.

The flexibility / complexity of Perl makes it easier to write code that another author / coder has a hard time reading.

PHP has a less confusing and stricter format without losing flexibility. PHP is easier to integrate into existing HTML than Perl. PHP has pretty much all the 'good' functionality of Perl: constructs, syntax and so on, without making it as complicated as Perl can be.

Perl is a very tried and true language, it's been around since the late eighties, but PHP is maturing very quickly.