Albert Barnes on Philemon 1:5

Hearing of thy love and faith. Either by Onesimus, who, after his conversion, would be disposed to state all that he knew that was favourable of Philemon, or hearing it by some other persons who had come from Colosse to Rome. The faith which is mentioned here refers to the Lord Jesus; the love, to the saints. The order in the Greek is indeed the same as in our version, but it is not unusual by synthesis, or uniting two or more things together, to arrange words in that manner. Thus Mt 12:22; "The blind and dumb both spake and saw;" that is, the blind saw, and the dumb spake. The meaning is, that he had strong faith in the Lord Jesus, and ardent love towards all who were Christians. See a similar declaration in Col 1:4.