Can a Foreigner in the Philippines be an SSS Member? 

Yes, if he or she is a permanent resident of the Philippines, or if he or she is a foreign employee working legally in the Philippines.

He or she must also comply with registration requirements for membership as Employed, Self-Employed or Non-Working Spouse.

Source:  Citizen's Charter of the Social Security System
1st Edition, December 2009

"Social security protection shall be provided to all residents of the
Philippines, citizens and non-citizens alike, regardless of creed, gender, age,
geographic location and economic status, especially the disadvantaged, so that
no one will become a burden to society."

Requirements for Registration:

Alien Certificate of Registration (ACR)

Bring other related documents, whatever is applicable to your residence or immigration status, in case additional papers are required:
-- Passport
-- Immigrant Certificate of Residence (ICR)
-- Board of Commissioner's (BOC) Order
-- Official Receipt of fees paid to the Bureau of Immigration

Note:  Bring xerox copies of documents

Photocopy of Passport includes biodata page, visa page, and latest arrival stamp