CLAIM: Paul commanded that the church of Colossae should exchange letters with the church of Laodicea (a city that was only ten miles away). This implies that Paul had another letter, which was authoritative and inspired that is now lost to us. Is this the case?
RESPONSE: There are two possibilities:
OPTION #1. This letter from the church of Laodicea is most likely the book of Ephesians. There is good evidence that Ephesians was a circular epistle—not being addressed to the specific church in Ephesus (see Introduction to Ephesians under “Audience”). If this is the case (it is the belief of this author), then it is likely that Paul is referring to his circular letter. We agree with Wright that this is the most likely view.
OPTION #2. This letter is truly lost. The NT and OT refer to books and letters that are now currently lost (1 Cor. 5:9; see comments on Joshua 10:13). If this is the case, then God did not superintend these books to be preserved.
 N. T. Wright, Colossians and Philemon: An Introduction and Commentary, vol. 12, Tyndale New Testament Commentaries (Downers Grove, IL: InterVarsity Press, 1986), 165.