I hope this is a coherent response...
You should not encounter too much difficulty learning Java if you already a solid foundation in the fundamental aspects of programming. There are some idiosyncrasies of PHP, however, that you need to be sure to look past when moving to another language.
Java is deeply object-oriented, and the Java development "culture" subscribes deeply to OO methodologies. PHP's OO was an afterthought added on, and is only beginning to fully mature. The PHP "culture" sometimes tends to care less about deep OO hierarchies because the language doesn't encourage it. PHP code tends to be an inconsistent mix of procedural and OO code, wherever the two are best suited. (This is not a criticism; PHP is my primary language these days too)
My suggestion would be this: Approach Java as though you are learning programming anew, though you already understand the important and fundamental flow control structures and atoms. Do not attempt to write Java code like it is a PHP web application, where the language sort of encourages a linear and procedural program flow. Use the time you spend learning Java to develop a strong sense of OO hierarchy and application architecture that you can spend years coding PHP without having to worry too much about.