In Paul: a Critical Life, Jerome Murphy-O’Connor defended the authenticity of Colossians and set its time during the Ephesian imprisonment in the summer of 53.
Paul wrote Colossians and sent it at the same time as the note to Philemon. Compare Philemon 23 to Colossians 4:10 ff. I don’t know of any scholar who questions that Paul wrote Philemon.
However Colossians is odd compared to other authentic letters of Paul. It has a style and a doctrine that come closer to Ephesians than other letters–and there are numerous reasons to think Ephesians does not fit with Paul’s missionary letters.
Most of those who have defended the authenticity of Colossians have put it late in Paul’s ministry to allow time for his style and theology to have evolved.
Murphy-O’Connor, however, adopted an alternative defense.
First, since Paul did not personally found the Colossian church (it was 120 miles from Ephesus and Paul had never been there), his style is understandably not as personal. This explains why Paul speaks generally and uses the words “all” and “everything” a lot. He is writing to the Colossians, but speaking universally.
But the main argument Murphy-O’Connor made was based on a comparison of Paul’s use of the hymn in Philippians 2:5 ff. and his use of another hymn in Colossians 1:15-20.
“Hymns and spiritual songs” played an important part in the liturgy at Colosse (3:16). These had a teaching function. So Paul used one of them. The original hymn in 1:15-20 was based on Jewish wisdom theology and spirituality and spoke of the Cosmic Christ.
Murphy-O’Connor thought that the problem at Colosse was that the church was tending toward an ethereal view of Christ that cut the connection between the earthly and cosmic Christ. Paul’s concern was that the Christ who stood above the world also stood in it.
So Murphy-O’Connor analyzed 1:15-20 to reconstruct the original hymn and then see how Paul used it and added to it. The following phrases, he thought, were Paul’s additions (p. 241):
“in heaven and on earth” (16b)
“visible and invisible” (16c)
“whether thrones or dominions” (16d)
“or principalities and powers” (16e)
“and he is before all things and in him all things hold together” (17)
“and he is the head of the body, the church” (18a)
“that in everything he might become pre-eminent” (18d)
“making peace through the blood of his cross through him” (20b)
“whether those on earth or those in heaven” (20c)
The effect of these is to affirm the historical and earthly without denying the spiritual and heavenly.
The major point, however, is that they parallel additions Paul made to the hymn in Philippians 2, where he added the phrases “in heaven, on earth, and under the earth” (twice) and “even death on a cross”.
This means it is most likely that the author of Philippians 2 also wrote Colossians–and at about the same time.
One additional nuance is that the original hymn in Philippians was already close to Paul’s view, so he made fewer additions. Another is that his additions to the Colossian hymn countered the worship of angels (2:18) as the Colossians stressed the vision of God surrounded by angels to the neglect of “the centrality of Christ in the real world” (p.243).
I am sure my summary of this argument is not as convincing as the full argument, which I found pretty convincing.