Luke in some ways leaves it to his readers to imagine what Paul was doing when he sets out a string of activities and travels in Acts 18:

18:18 Paul, after staying many more days in Corinth, said farewell to the brothers and sailed away to Syria accompanied by Priscilla and Aquila. He had his hair cut off at Cenchrea because he had made a vow. 18:19 When they reached Ephesus, Paul left Priscilla and Aquila behind there, but he himself went into the synagogue and addressed the Jews. 18:20 When they asked him to stay longer, he would not consent, 18:21 but said farewell to them and added, “I will come back to you again if God wills.” Then he set sail from Ephesus, 18:22 and when he arrived at Caesarea, he went up and greeted the church at Jerusalem and then went down to Antioch. 18:23 After he spent some time there, Paul left and went through the region of Galatia and Phrygia, strengthening all the disciples.

Beverly Gaventa: “Paul does not work as a solitary entrepreneur but plays a role in the one witness that God began in Jerusalem and effectively continued from Antioch” (263; Acts Abingdon New Testament Commentaries
).