Paul and Timothy, slaves of Christ Jesus, to all the saints in Christ Jesus being in Philippi, together-with the overseers and deacons: Grace to you and peace from God our Father and the Lord Jesus Christ. I am giving-thanks to my God upon every remembrance of you, always in my every petition for you all making the petition with joy on-the-basis-of your partnership for the good-news from the first day until the present,Philippians 1:1-5 - https://www.biblegateway.com/passage?search=Philippians 1:1-5&version=DLNT
Is a partnership for the good-news (the spreading of the Gospel we all have a commission to do) from the “first day” until the present not referring to “all the saints in Christ (Messiah) Jesus”? How many Philippians called Jesus the Messiah on “the first day? None, they weren’t there on the first day. Not even Paul or Timothy were calling Jesus Messiah on the first day.
He’s obviously talking to all Gospel partners (saved people) who are making the petition (not just a few specific deacons).