I know it was a Portuguese colony, but why did the Philippines accept Christianity with such open arms? Why didnt some other Asian countries accept it the way the Philippines has?
What other previous colonial countries in Asia converted to Christianity in mass like the Philippines has?
The Philippines was a Spanish colony, not Portuguese.
They were conquered and colonized by Spain, so they didn't have a choice.
And no other Asian country was colonized by Spain.
The Spanish colonial project started early compared to other European nations, in 1492. And it was undertaken in the same spirit as the Reconquista, which had only just finished driving out the Muslims from Spain that same year. So the colonizing project had a strongly religious strain: spreading and converting pagans to Christianity.
The Philippines that the Spanish encountered was not highly developed and it was not densely populated. There were only some 750,000 inhabitants. People lived in small, autonomous social units, the barangays, which numbered some 100-500 people. The barangays did not have much social stratification and practiced subsistence farming.
They were no match for the Spaniards, just as the southern-most island of the Philippines, Mindanao, had been no match for the more advanced Muslims. The Spaniards soon sent missionaries throughout the islands, using the same methods of conversion and management as they did in Latin America: they had reducciones and they learned and taught in the native languages. Since the Manila galleon trade with New Spain (Mexico) was set up soon after the Spanish arrived, most Spaniards confined themselves to Manila, where they lived well. In all of the rest of the country up until the 19th century, really the only Spaniards Filipinos saw were priests. This explains the common Filipino summary of their history as "400 years in a convent and 50 years in Hollywood.”
EDIT: typos and clarity