In Philippians 1:13, Paul says it had become clear to whom that he was in chains for Christ?

Answer: The whole palace guard

Paul says his imprisonment advanced the gospel: it became clear throughout the whole palace guard that he was in chains for Christ.

“Now I want you to know, brothers, that my circumstances have actually served to advance the gospel. As a result, it has become clear throughout the whole palace guard and to everyone else that I am in chains for Christ.”— Philippians 1:12-13 (BSB)