Rick Phillips has written an article that should help clear the air about whether one should privately phone the author of a book or article before offering public criticism of their work. Rick offers 4 reasons why Matthew 18 is not a valid objection, and you can read his explanations at Reformation 21.
1. Matthew 18 establishes a procedure for dealing with personal sins, not public debate.
2. Just as private matters should be handled privately, public matters should be handled publicly.
3. When an author happens to be an officer under confessional vows to the Church, writings that impact the application of those standards are a public, not a private matter.
4. We must realize that teaching and publishing entails a public responsibility that invokes public scrutiny and criticism.