Did Paul ever meet Jesus face to face during Jesus' earthly ministry?
No. Paul did not have a face-to-face confrontation with Christ during His earthly ministry. The context states Paul had quite a few such encounters after the work of the cross, and Paul claims he saw the Lord face to face and the Lord revealed these things to him.
Les explains that Jesus’ words to Paul came from the ascended glory after the work of the cross. He notes there is no direct communication between Jesus and sinful men once He ascended back to glory, except this man, and Paul claims over and over that he saw the Lord face to face and that the Lord revealed these things. Les points to Galatians, where Paul never had a face-to-face confrontation in Christ and His earthly ministry, but had quite a few after the cross. He contrasts the pre-cross approach through animal blood with the post-cross approach through Christ’s blood, saying the gospels are before Christ is crucified and contain no shed blood of Christ. Les also notes Paul knows Christ crucified, pointing to 1 Corinthians 1:18 and Galatians 1:11.