Think of PHP as a really amazing shell scripting language. Just as shell scripts can be glue for all the powerful UNIX utilities, PHP gives you APIs for just about any useful library you might need for web work. You won't be able to use your fancy Python chops for things like generators or itertools, but with luck instead you'll be running a bunch of powerful well-designed existing C code with a few function calls. Of course, a significant project will require a bunch of data & logic in PHP...
Also, the PHP source code is quite readable, for those times when the good online reference manual doesn't help.
Also, the PHP source code is quite readable, for those times when the good online reference manual doesn't help.