PHP is not developer friendly and does not encourage a good design of your software. That said, PHP is a very newbie friendly language, but eventually you will run into some weirdness of php.

PHP is legacy software. it is full of backwards compatability, that does not even work for some things.

PHP is designed badly and the language is full of hacks to add functionality it should have had ages ago. Take exceptions for example, they were added in php5, but they have very little use for the built-in php functions. Just a few use them.
An other good example of bad design; PHP does not know libaries in its main distribution. Every function is availlable at any time in PHP. This may seem like a thing that’s very handy, you’ll never have to import a specific library to do your things, but actually it is a curse. An example, you made your own scandir function a long time ago. As PHP “progressed”, the function scandir was added to the builtin functions. Great, but your script just broke. PHP does not allow you to redefine a built-in function. If this function was added to a library, there would not have been a problem.
The lack of namespaces is a big problem, new functions need weird names to avoid conflicts with older ones. The default (and only?) namespace is too huge.
PHP lacks modules. You have to recompile php entirely to add a feature. Besides the time it takes to compile, sysadmins wont be all to happy about maintaining own packages. Every tiny update requires a complete rebuild of PHP. Why do you even want all available function available to you all the time?

PHP had its best time. Avoid PHP if you can, learn Python, Ruby or even c#.