What period of Paul's ministry does the book of Galatians cover?
The book of Galatians covers the period of Paul's ministry when he was roaming the Roman Empire, establishing churches, before the interruption that came at Acts 28, when he was arrested and taken to prison in Rome. It addresses that earlier period.
Les teaches that Galatians was written during the period Paul was constantly referring to Abraham, using the allegory of Isaac and Ishmael as pictures of Law and Grace, flipping back into the Old Testament, using the Jew as examples, and appealing to the Jew to come out of blindness and legalism into the Light of God's Grace. That covered the whole period while Paul was roaming the Roman Empire, establishing churches. But now with Acts 28 there is an interruption in Paul's ministry: he is arrested and taken to prison in Rome. So Galatians addresses that earlier, pre-imprisonment period of Paul's ministry.