This is modest from the outside, as the Ottomans would not permit non-Muslim religious buildings to rival the mosques. The interior is lavish but its chief importance is as the senior Eastern Orthodox church. Their Patriarchate has been housed here since 1586 when they were ejected from Agia Sophia.

The Ecumenical Patriarchate of Constantinople is one of the autocephalous churches of the Eastern Orthodox Church. It is headed by the Ecumenical Patriarch of Constantinople. Because of its historical location as the capital of the former Eastern Roman Empire and its role as the mother church of most modern Eastern Orthodox churches, Constantinople holds a special place of honor within Eastern Orthodox Christianity and serves as the seat for the ecumenical patriarch, who enjoys the status of primus inter pares among the world's Eastern Orthodox prelates and is regarded as the representative and spiritual leader of Eastern Orthodox Christians. Phanar , the name of the neighbourhood where ecumenical patriarch resides, is often used as a metonym or shorthand for the Ecumenical Patriarchate of Constantinople. The Ecumenical Patriarchate of Constantinople promotes the expansion of the Christian faith and Eastern Orthodox doctrine, and the ecumenical patriarchs are involved in ecumenism and interfaith dialogue, charitable work, and the defense of Orthodox Christian traditions. Prominent issues for the Ecumenical Patriarchate's policy in the 21st century include the safety of the believers in the Middle East, reconciliation of the Eastern Orthodox and Catholic churches, and the reopening of the Theological School of Halki, which was closed down by the Turkish authorities in 1971.