Metropolitan Hilarion of Volokolamsk
The apostolic Church did not have special vestments for sacred serving. Christ celebrated the Mystical Supper in regular clothing and the Apostles wore their everyday clothes during the celebration of the Eucharist. As a result, however, of the Eucharist being transformed from a meal into a ceremonial service, everyday clothing came to be treated as sacred. When that clothing ceased to be commonly used, it was preserved in the usage of the Church. Different clothing, having special liturgical purposes, appeared as well.
…The most ancient component of the liturgical vestments of bishops and priests, besides the sticharion, is the phelonion. Saint Simeon of Thessalonica refers to this garment as fainolion and writes that it “reveals (fainei) the highest strength and enlightenment bestowed from on high”. In apostolic times the phelonion was a sleeveless wool coat used as an outer garment. The phelonion is mentioned by the Apostle Paul (2 Tim. 4:13) as an article of everyday clothing. There were various styles of phelonions and they could be worn on one shoulder or on both so that the front ends were pulled forward. The phelonion could be four-sided with tassels on the sides and fringes. However, in the Christian tradition, the most widespread type of phelonion had the shape of a bell, with a circular opening for the head. It was donned over the head and covered the entire body of the man wearing it. It could have the same length in the front as in the back or it could run higher in the front than in the back. In some cases, the phelonion was shorter on the side of the right arm and longer on the side of the left arm.
At a later time, when hierarchs began to wear the sakkos instead of the phelonion, the phelonion was preserved as a basic liturgical vestment for priests. The phelonion which is used in the Greek Church up to the present day is similar to those depicted in Byzantine frescoes. In the Russian Church in the Synodal period, the phelonion acquired a slightly different shape. In the front it was cut from the bottom in such a way that the priest’s arms remained uncovered and in the back its top end was raised. This type of phelonion is worn today in the majority of the churches of the Russian Orthodox Church. (Orthodox Christianity Vol. III, The Architecture, Icons, and Music of the Orthodox Church by Metropolitan Hilarion Alfeyev. pp. 94-96)