PHP isn't difficult in the sense that it makes you think hard, like a more terse language like Lisp or something lower-level like assembler. It's difficult in the sense of being annoying and causing extra work, like when you have to look up a function you can't remember because there are way too many and no consistent naming convention. Or when you forget that you have to quote the key in a hash, like $hash['key'] -- except when you don't, like when it's being interpolated in a string between double quotes. Or when you wish you could use Perl's natural-sounding backwards syntax, like next unless $count;
Unpleasant and time-consuming, but not really difficult. If you're capable of programming in Perl, you're certainly capable of using PHP. It has C-style syntax, and it even borrowed Perl's regular expressions (although not every feature of them), so many things will be familiar. Just don't expect it to be as flexible or fun to write in.