The letter from the Apostle Paul (and Timothy, 1:1) to the church at Philippi seems to have been written from Rome while Paul was imprisoned.
1. Paul is in prison, 1:12-16,19ff.
2. Paul mentions the palace (1:13) and Caesar's household (4:22).
3. During the imprisonment at Rome, Paul faced two possibilities - life or death. Compare that to 1:19-26.
4. Christians in Macedonia (where Philippi is) were active in the collection for the saints at Jerusalem (II Cor. 8:1-5; 9:14). Silence about it in this letter would indicate it was already a thing of the past.