Or HaChaim on Genesis 39:22/אור החיים על בראשית ל״ט:כ״ב

1 הוא היה עושה, which he was doing. Onkelos translates: על מימריה הוה מתעבד, that what was done inside the jail was done at Joseph's instructions. If that was so, why does the Torah not say so outright, i.e. ועל פיו היו עושים? Perhaps the Torah wanted to hint that though Joseph enjoyed great authority within the jail, he did not use it to make the other inmates feel as if he dictated to them. He did not claim any special privileges for himself either. All this was evidence of his good character.