Learning Perl is usually as hard as you make it. Some people can't get over the fact that it's a different language so they try to do things like they would in a different language.
Your ease of learning will also depend on how you decide to learn it. There are a lot of bad tutorials and books out there that guess at some things in Perl. There are really only a handful of concepts that you need to know, but if you don't pick those up you're going to have a lot of pain. Most tutorial writers seem not to know those concepts. Of course, I recommend my book Learning Perl, if not live Perl training from an expert whom you can ask questions and get some guidance. It's very important to not be lead astray from the start. With a good foundation, you can branch out on your own.
A lot of people think learning a language means learning the syntax, but that's just kindergarten. You really need to learn the libraries and tools of a language ecosystem. Perl is mostly popular because of everything it has despite its syntax, including a very dedicated community. You aren't going to learn that stuff from books (although I try to impart some of that in Mastering Perl and Effective Perl Programming). That's mostly a matter of experience.
If you're doing PHP, I might infer that you are doing web stuff. In that case, check out Catalyst. It might not be the Perl web framework you end up using, but it's a good place to start if you don't have an existing preference. Get the Apress book, not any other one.
However, it's probably pretty dumb for a company to take a bunch of people who don't know Perl yet and make them into a Perl shop quickly. I've worked for a few companies that would lie and cheat to get business then scramble to develop the skills they needed to do the project. That's a pretty dumb way to run a business because almost no one likes working in that environment.
You really need someone who's familiar with the landscape to really use Perl (or any language) effectively. You might be able to find a Perl mongers group near you where you can find some experienced people. Find some Perl friends and get to some Perl events if you can.
Perl is a great language to know, but if your boss is expecting a proficient Perl team pumping out solid code in a month by starting from scratch, he's probably moonlighting as one of the characters of FantasyLand.