Our next two references to “gospel” in Philippians are found at 1:12 and 1:16. Here they are in context:

12 Now I want you to know, brothers, that what has happened to me has really served to advance the gospel. 13 As a result, it has become clear throughout the whole palace guard  and to everyone else that I am in chains for Christ. 14 Because
of my chains, most of the brothers in the Lord have been encouraged to
speak the word of God more courageously and fearlessly.

15 It is true that some preach Christ out of envy and rivalry, but others out of goodwill. 16 The latter do so in love, knowing that I am put here for the defense of the gospel. 17 The
former preach Christ out of selfish ambition, not sincerely, supposing
that they can stir up trouble for me while I am in chains. 18 But
what does it matter? The important thing is that in every way, whether
from false motives or true, Christ is preached. And because of this I
rejoice.

Two words coexist for Paul: gospel and Christ. Christ is the gospel and the gospel is Christ.

Paul is in prison for the gospel, that is for his preaching of Christ. And others are encouraged by his chains to preach the gospel even more.

Not everyone, Paul says, preach the gospel out of compassion and love; some do. And Paul is so confident in Christ and the gospel that he is happy when others preach Christ out of bad motives. Why? Christ gets preached.

The gospel is the work of God to restore cracked Eikons through Christ and any preaching that is not about the saving work of Christ is not gospel preaching.