Opportunities range from formal balls to American style barbecues with country line dancing. No Census figures exist for US citizens overseas. US Consular Services reports 105,000 Americans in Philippines. Other numbers not known, but there are many nationalities represented in the expat community. Not as casual as dress-down days at some US corporations, but not a coat and tie.
Women tend to wear more traditional business attire.
Extremely casual wear is not generally seen in public. Filipinos are modest in their dress and not excessively casual in public. Remember it is always summer in the Philippines, so lightweight cotton clothing is desirable. Very good doctors and dentists can be found. Many doctors frequented by expats have done some or all of their training in the West.