The earliest creed is much more about fidelity than it is about doctrinal formulas. The lordship of Christ is about his authority in the life of the Christian rather than that person's beliefs about the particularities of Christ's nature:
The confession ‘Jesus is Lord” is at once the earliest Christian creed and an acknowledgment of Jesus’ divinity and sovereignty. Paul used that designation only three times in his letters and each time with worshipful sincerity and awe. The other two are found in Romans 10:9 and 1 Corinthians 12:3. This was said to be the essential confession each convert repeated at baptism. All the Philippians had made this same confession. All later creeds of the Christian church derived from it. There was - and is - nothing more that needs to be said as a statement of faith.
For Paul, and for the Philippians too, this would have been the utmost in civil disobedience and high treason. In those times the only person for whom this could be said was Caesar himself. “Caesar is Lord” was the oath taken by every Roman citizen. For all time, this confession “Jesus is Lord” commits the one who says it sincerely to a life in which Jesus reigns supreme and so lives day by day to fulfill the will and purpose of God.