if I were you - if I was you - which is correct?

Conditional sentences (if-clauses, main clauses)

Summary

Type I

Type II

Type III

Special types and structures

Mixed Conditionals

if I were you

will and would in if-clauses

Replacing if - Omitting if - if vs. when - in case vs. if

Conditional sentences (if) - Complex Test 1

Exercises - Conditional sentences (if)

The word were in the phrase if I were you is special form. It is known as the subjunctive mood (from the grammatical point of view).

Today you also find the phrase if I was you. Here the Simple Past form of be is used. But there are people who say that this phrase is incorrect and would never use it (mainly Americans). Others say that this phrase can be used.

If I were you I would phone him. - subjunctive mood 
If I was you I would phone him. - Simple Past