My Future as a Developer

Well from my observation of last couple of years I would say that salaries go like this:
Java > C# > PHP, but note that this is a bit generalized and localized statement of mine so don't give too much thought into it.
But I would say that yes the PHP is commonly the lowest paid among those, nevertheless I must say I encounter more positions for PHP developers then for a C# or Java developers.
I would also say that the truth is that big brands avoid script languages, it is just because it usually ends up requiring much more effort in enterprise solutions which results in inefficient architecture...

But the main point is what type of environment would you like to work in, well if your goal is some big IT industry then yes you should probably switch, but note that there is a bright future in PHP as well (it just usually does not include big names). People often like to say that big names also use PHP, Facebook for example, but the truth is that when push comes to shove the company will do the necessary switch just like Facebook did ...

You mentioned that you are familiar with OOP, MVC and those languages, then I believe you will not have a hard time in learning them. I mean the concepts are pretty much the same and the syntax will come on its own, so all you actually need is some practice.
I would also recommend you some programming aptitude tests from TestDome which could help you out in your learning phase. I find them to be a great resources for practising some real life coding scenarios, for example you can first try these PHP coding tests to get familiarized with the testing style. After that you can proceed on with the language that you want to learn; these are C# coding tests and these are Java coding tests.