First, don’t feel too bad — phishing attempts are getting very, very sophisticated. I haven’t fallen for one yet, but I’ve come darned close a time or two.
But be prepared for a painful recovery if the phishing was successful.
How to tell if you’ve been phished depends on where in the process you are: looking at an email, after clicking a link in the email or other source, or some time thereafter.
What to do after that depends on what information you gave in response to the phishing attempt.