This is from the website of the Philippine Embassy in Korea…
Application for Retention and Reacquisition of Philippine Citizenship may be filed at the Philippine Embassy in Seoul pursuant to Republic Act No. 9225 otherwise known as the “Citizenship Retention and Reacquisition Act of 2003 and its Implementing Rules and Regulations.
All natural born Filipinos who have lost their Philippine citizenship due to naturalization as a citizen of another country may file a Petition for Retention and Reacquisition of Philippine Citizenship and may include in the Petition, their unmarried children, below eighteen (18) years of age .
1. Accomplished Application Form
2. Accomplished Petition for Retention and Reacquisition of Philippine Citizenship
3. Six (6) recent 2×2 colored pictures. front view over white background
4. Two (2) recent 2×2 colored pictures, left and right side view
5. The original and two photocopies each of the following documents. The original documents must be shown to the Embassy for verification:
• For those born in the Philippines, NSO authenticated birth certificate or old Philippine passport . For those born abroad, Report of Birth (filed with the Foreign Service Post) or foreign issued Birth Certificate
• Certificate of Naturalization in a foreign country
• Foreign issued passport
• Marriage Certificate for married women (translated to English)
• For Bureau of Immigration registered applicants :
– Alien Certificate of Registration (ACR)
– Immigrant Certificate of Residence (ICR)
6. Fee of US $ 50.00 or KW 67,100 and US$ 25.00 or KW 33.550 for each dependent
Upon submission of the above requirements, the Embassy will evaluate the application and schedule the date for the Oath of Allegiance (in prescribed form) before the consular officer. The Embassy will issue an Order of Approval and an Identification Certificate. Thereafter, the applicant may schedule an appointment for the application of an ePassport at the Philippine Embassy.
I am not really sure if this is applicable for all Filipinos who are Korean citizens. From what I remember, only Filipinos who had their application for Korean citizenship approved from July 1, 2010 may be eligible to apply for dual citizenship. I could be wrong though.