I had sued my business partner for fraud, he has retained an attorney to represent him in the lawsuit. I have spoken to his attorney on the telephone about another business matter I had in the past but I never retained him. Is this considered conflict of interest?
Conflicts of interest are regulated by the Rules of Professional Conduct. Rule 1.8 is the general rule. It does not appear from your description that would be a conflict, since you said that what you spoke to the lawyer about was a matter unrelated to the suit that you have now brought.
You can read the RPC provisions at: http://www.courts.wa.gov/court_rules/?fa=court_rules.list&group=ga&set=rpc