>Hi everybody,
>
>I am wondering if there is some online dictionary where I can check if I used the right preposition in a phrase? Say, often after I've written a phrase I have a feeling that something is not exactly right. I want to be able to quickly check myself.
>
>Thanks in advance.

That's not going to be an easy task. You know how to diagram a sentence? Might look here: http://www.english-grammar-revolution.com/prepositional-phrase.html

There is a preposition in a phrase - but there is also something called a prepositional phrase.