Among the titles under which Mary is venerated in the Philippines, two are particularly prominent: the Immaculate Conception and Our Lady of the Rosary. The invocation of the Immaculate Conception goes back to the year 1578 when Pope Gregory XIII in a Bull issued on February 6 decreed that the Manila Cathedral should be erected under the invocation of the Conception of the Blessed Virgin Mary. Clement VIII decreed on 13 August 1595 that the Cathedrals of Nueva Segovia and Caceres also be erected under the same title of the Immaculate Conception. Moreover, one of the three ships that reached the Philippines in the first voyage of Magallanes in 1521 was the "Concepcion," named after the Immaculate Conception, together with the ships "Trinidad" and "Victoria." Hence the Islands before being named Filipinas, and even before the name of Christ had begun to be preached, saw on these shores the name of Mary under her title of the Immaculate Conception.
The Immaculate Conception , whose feast falls on December 8, remains the principal Patroness of the Philippine Islands. After the suppression of several Church holydays in the Catholic Calendar of the Philippines, still her feast stays as one of the three holydays of obligation during the year, the other two being Christmas and January 1, when the Solemnity of Mary, Mother of God, is celebrated.
From: ANG MAHAL NA BIRHEN
Mary in Philippine Life Today
A Pastoral Letter on the Blessed Virgin Mary
Catholic Bishops' Conference of the Philippines
February 2, 1975
Photo source: The blog of Marwil N. Llasos OP. This blog is a rich source of Marian images and apologetics. I also recommend the following article from this blog: The Dominicans in the Philippines and the Immaculate Conception.