What is the diffrence between phrases and clauses?
A clause will have a subject and a verb. An independent clause is simple sentence.
A phrase is a group of words that serve one function: a noun phrase (which can be the subject or object), an adjectival phrase (which describes a noun), an adverbial phrase, etc.
EDIT: Oh, and welcome to Using English!
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.