When Paul says, "my true companion," the word "you" is singular. Paul does not say the name of the person. He calls him that to show he worked with Paul to spread the gospel. (See: [[rc://en/ta/man/translate/figs-you]])
Paul uses the word "joy" to mean that the Philippian church is the cause of his happiness. A "crown" was made of leaves, and a man wore it on his head as a sign of honor after he won an important game. Here the word "crown" means the Philippian church brought honor to Paul before God. Alternate translation: "You give me joy because you have believed in Jesus, and you are my reward and honor for my work" (See: [[rc://en/ta/man/translate/figs-metonymy]])