Did Paul claim to be the foundation or the one who laid the foundation?
Paul claimed to be the one who laid the foundation, not the foundation itself. He called himself a wise master builder who, by God's grace, laid the foundation. The passage explicitly states he does not say he is the foundation; that distinction is carefully maintained.
Les explains that Paul had to constantly defend his apostleship because it was under constant, Satanic attack. The Holy Spirit inspired Paul to claim that, because of the grace of God, as a wise master builder, he laid the foundation. Les emphasizes that Paul does not say he is the foundation, and he is careful to make that distinction. This comes in the context of divisions in the Corinthian church, where some were following what Jesus said, what Peter said, what Apollos said, and a few were staying with Paul. Paul's role was to lay the foundation, not to be the foundation.