Why is St. Philip the Evangelist called "the evangelist"?
In what way St. Paul uses the word "evangelist" may not be in the sense of writing a Gospel.
"What is an evangelist?"
An evangelist is someone who proclaims good news; in other words, a preacher of the gospel or a missionary. A person with the gift of evangelism is often someone who travels from place to place to preach the gospel and call for repentance. The human authors of the four Gospels—Matthew, Mark, Luke, and John—are sometimes called “the Evangelists” because they recorded the ministry of Jesus Christ—“good news,” indeed.
Ephesians 4:11–13 states, “Christ himself gave the apostles, the prophets, the evangelists, the pastors and teachers, to equip his people for works of service, so that the body of Christ may be built up until we all reach unity in the faith and in the knowledge of the Son of God and become mature, attaining to the whole measure of the fullness of Christ.” In Acts 21:8 Philip is named as an evangelist, and in 2 Timothy 4:5 Paul exhorts Timothy to do the work of an evangelist. These are the only three uses of the word evangelist in the entire Bible. Other people could be considered “evangelists” in that they preached the good news, including Jesus Himself (Luke 20:1) and Paul (Romans 1:15), but Philip is the one person specifically called an evangelist in Scripture.
Philip had been one of the seven deacons chosen so that the apostles could do their work of teaching and prayer (Acts 6:3). Evidently, Philip had settled in Caesarea and had lived there for some 20 years before Paul arrived in Acts 21. Philip’s previous evangelistic work was in Samaria (Acts 8:4–8). He “proclaimed the Messiah” to the Samaritans (verse 5) and performed miracles, including casting out demons and healing paralytics. It is noteworthy that Philip performed water baptism in the name of Jesus, but the baptism of the Holy Spirit did not occur until the apostles came to Samaria.
Peter and John’s presence in Samaria and the Spirit’s indwelling of the believing Samaritans (Acts 8:17) confirmed Philip’s ministry there. As an evangelist, Philip had preached the gospel, and, when the Samaritans believed it and received the Spirit, they were welcomed into the church. Where there had previously been division and animosity between Jews and Samaritans, there now existed the spiritual bond of love (Colossians 3:14). Philip’s trailblazing efforts laid the foundation for his hearers to receive the Holy Spirit by faith. The evangelist’s pre-work unto salvation is what those called evangelists have done ever since.
Philip’s ministry as an evangelist continues in Acts 8 as he is led by an angel to go the desert road to Gaza. On the road he meets an Ethiopian eunuch—a court official to the queen of Ethiopia. Philip opens the man’s understanding of the Word of God, and the eunuch is saved. Philip baptizes the man, and the Holy Spirit snatches Philip away (Acts 8:39). Philip later “appeared at Azotus and traveled about, preaching the gospel in all the towns until he reached Caesarea” (verse 40). Everywhere he went, Philip shared the gospel. That’s what evangelists do.
There may be only a few historical hints as to why St. Philip is called the evangelist. It is not impossible that the term evangelist had anything to do with writing a gospel. It may be, in fact, that that he had a great influence on the evangelization of the Ethiopian nation, as well as to the fact that he preached the Gospel in many areas. Thus he was a true evangelist. In modern days do we not hear Billy Graham being referred to as an American "evangelist".
But first let us look at the New Testament:
Philip bore a Greek name. He is first mentioned in the Acts of the Apostles (6:5) as one of "Seven Deacons" who were chosen to attend to certain temporal affairs of the church in Jerusalem in consequence of the murmurings of the Hellenists against the Hebrews.
After the martyrdom of Saint Stephen he went to "the city of Samaria", where he preached with much success, Simon Magus being one of his converts. He afterwards was told by an angel of the Lord to go to the road between Jerusalem and Gaza. There he instructed and baptized the Ethiopian eunuch; next he was "caught away" by the Spirit and "found at Azotus" (Ashdod), and then "pass[ed] through he preached in all the cities till he came to Caesarea" (Acts 8).
Here some years afterwards, according to Acts 21:8–9, where he is described as "the evangelist" (a term found again in the New Testament only in Ephesians 4:11; [2 Timothy 4:5), he entertained Paul the Apostle and his companion on their way to Jerusalem; at that time "he had four daughters which did Prophecy". - Philip the Evangelist
In Catholic tradition he converted the Ethiopian eunuch of Queen Candace of Ethiopia and preach the Gospel wherever he went.
Probably an Hellenized Jew. One of the seven Jerusalem deacons mentioned in the canonical Acts of the Apostles. Preached and performed miracles in Samaria, converting many including the magician Simon Magus. Commanded by an angel, he travelled from Jerusalem to Gaza. Converted and baptized the eunuch of Queen Candace of Ethiopia. Transported to Azotus, he preached throughout the region, finally returning to Caesarea where he lived with his four daughters, virgins with the gift of prophecy. Met with Saint Paul the Apostle on his last journey to Jerusalem. Some traditions say be became bishop of Tralles (modern Aydin, Turkey).
St. Philip the Deacon was a true evangelist.