I commend to you our sister Phoebe, a servant of the church at Cenchreae...
Romans 16:1 ESV

From the very broad use of diakonos throughout the New Testament, it appears to apply to any role in which one person serves the needs or purpose of another. I don’t think Paul ever intended to create an office in the body of Messiah bearing the title “deacon”. Rather, there are many roles that people fill in service to the body, with or without any inherent authority, and therefore can all be called deacons.

Sometimes people are clearly commissioned to be servants for a specific purpose--as is the case of Timothy (1 Thessalonians 3:2), Stephen (Acts 6:1-6), and the servants of 1 Timothy 3--but more often, people are simply being helpful, as is likely the case of Phoebe in Romans 16:1. Indeed, I think it would be better if we removed the word deacon from our vocabulary altogether and simply translated diakonos as “servant” in every case.