what religion is practiced in these regions?
Islam, Buddhism and Christianity are some of them.
Southeast Asia
Countries in Southeast Asia practice many different religions. By population, Islam is the most practised faith, numbering approximately 240 million adherents, or about 40% of the entire population, concentrated in Indonesia, Brunei, Malaysia, Southern Thailand and in the Southern Philippines. Indonesia is the most populous Muslim-majority country around the world.

There are approximately 205 million Buddhists in Southeast Asia, making it the second largest religion in the region, after Islam. Approximately 38% of the global Buddhist population resides in Southeast Asia. Buddhism is predominant in Vietnam, Thailand, Laos, Cambodia, Burma and Singapore. Ancestor worship and Confucianism are also widely practised in Vietnam and Singapore.

Christianity is predominant in the Philippines, eastern Indonesia, East Malaysia and East Timor. The Philippines has the largest Roman Catholic population in Asia. East Timor is also predominantly Roman Catholic due to a history of Portuguese rule.
where are the philippines located on the world map it is in Southeast Asia, situated in the western Pacific Ocean. was it colonised by anyone? Yes, by a Spanish explorer "Miguel López de Legazpi" can you name some places that come under the southern region you mentioned? China, India and Australia are some of them.
wiki:19581165
Southeast Asia [SEP] Religion
Countries in Southeast Asia practice many different religions. By population, Islam is the most practised faith, numbering approximately 240 million adherents, or about 40% of the entire population, concentrated in Indonesia, Brunei, Malaysia, Southern Thailand and in the Southern Philippines. Indonesia is the most populous Muslim-majority country around the world. There are approximately 205 million Buddhists in Southeast Asia, making it the second largest religion in the region, after Islam. Approximately 38% of the global Buddhist population resides in Southeast Asia. Buddhism is predominant in Vietnam, Thailand, Laos, Cambodia, Burma and Singapore. Ancestor worship and Confucianism are also widely practised in Vietnam and Singapore.