no church but you partnered with me in the matter of giving: Paul chose not to accept money from the Corinthians, because he was concerned it might harm how they understood the good news about Jesus (1 Corinthians 9:11–18; 2 Corinthians 11:7–12). But he had no such concern with the Philippians.
in the early days of the gospel: This refers to when Paul first preached the good news in Philippi (See Acts 16:11–40).