Hello Jordz,
The first step is to confirm your Spanish origins. You mention your father was Spanish and that his name appears in your birth certificate. Do you know if he was a Spanish citizen at the time you were born? If that is the case and you obtain a copy of his birth certificate and passport or DNI, I believe a visit to the embassy in Manila is worth it. In the event you are considered originally Spanish, you will be able to apply for the Spanish nationality by option easily.
As the grandson of a Spanish citizen, you would be able to apply for the Spanish nationality after one year holding a residence permit in Spain.
Regards,
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