As CountZero points out, "LAMP" just refers to a combination of Linux, Apache, MySQL and a web-dev scripting language which will work with them (PHP, Perl, or Python).

But here's an opinion on PHP anyway, since there could well be many "LAMP" jobs that do require PHP specifically: I had to learn php for a job that required writing a mediawiki extension (since mediawiki is in php). IMO, it is not as nice a language as perl -- regexps are ridiculously awkward by comparison, etc (of course, they are even more awkward in compiled languages). However, I would disagree that "PHP is not a decent language in general". Easy to say, but mostly just ignorance and hyperbole. Such arguments and attitudes are a waste of time, ie, ignore excessive naysayers.*

PHP borrows most of it's syntax from perl and C++. I found it very easy to pick up. Partially this is because the official PHP online documentation is terrific -- one area I would say the community is clearly light years ahead of "us"; perldoc.org, CPAN, & POD stuff are moldy old scrolls by comparison.

Also:

• The more tools in your toolbox the handier you will be.
• Learning new languages is fun and enlightening.

Of course, that can lead to the "Jack of all trades, Master of none". But it takes all kinds. Once you get comfortable, the language takes kind of a backseat to the thinkin' and programmin'. I'm happy to be back doing perl stuff, but I'm sure I'll end up doing php work again in the future. $0.02

* unless they are naysaying MS windows, in which case it is probably all true and worse ;)