Account of His Martyrdom
According to a devotional account (the only substantive narrative located for him), Eusebius came forward of his own free will before the prefect of Phoenicia and rebuked him for persecuting the Christian community, reportedly asking what senseless deed he was doing in harrying the flock of Christ.
The same account relates that this bold declaration angered the prefect, who ordered Eusebius suspended and his body lacerated, and that he bore his sufferings with striking composure. The prefect, said to be confounded by his endurance, finally ordered him beheaded. Because this narrative is devotional rather than documentary in character and carries no date, named official, or scholarly citation, its details should be read as tradition.
Catholic reference works give a parallel but sparser outline, describing Eusebius as openly declaring himself a Christian during an unspecified persecution in Phoenicia and being tortured and put to death; they classify his recognition as pre-Congregation (predating formal canonization procedures).
Identity and Distinct Saints
Eusebius of Phoenicia should not be confused with the Martyrs Eusebius, Nestabus, and Zeno of Gaza, who are also commemorated on September 21 but are distinct individuals associated with the persecution under Julian the Apostate in the fourth century.
On September 21 the Church additionally commemorates several other saints, among them Martyr Priscus of Phrygia, Hieromartyr Hypatius of Ephesus and the Presbyter Andrew, the Apostle Quadratus of the Seventy, and the twenty-six Monastic Martyrs of Zographou on Mount Athos.
Source Coverage
This is a genuinely obscure saint. He has no dedicated article on Wikipedia or OrthodoxWiki, and the chief reference calendars (OCA, OrthodoxWiki) record only his name and feast. The fullest available narrative is a single devotional post, with a brief stub entry in Catholic reference works citing the Book of Saints of the Monks of Ramsgate and Our Sunday Visitor's Encyclopedia of Saints.
The region of origin given here reflects the ancient province of Syria Phoenice; his era and century remain undetermined from the surviving sources. The thinness of this profile is itself an honest reflection of the record.