ISB ~ Colossians 4 v16

read among you:Most likely in a liturgical context. Very early on Paul’s epistles were recognized as authoritative and even scriptural (2 Pet 3:15-16). the letter from La-odicea: The identity of this letter is uncertain. It may be (1) a letter that Paul wrote to the La-odicea Church that has not survived or (2) another of Paul’s epistles that was circulating in the region, possibly Ephesians. In any case, the Colossians are encouraged to exchange letters with the neighboring La-odiceans.

See introduction to Ephesians:Destination.