I am not a lawyer. This is not legal advice, just my personal opinion.
Revised penal code of the Philipines, article 247:
Art. 247. Death or physical injuries inflicted under exceptional circumstances.
Any legally married person who having surprised his spouse in the act of committing sexual intercourse with another person, shall kill any of them or both of them in the act or immediately thereafter, or shall inflict upon them any serious physical injury, shall suffer the penalty of destierro.
If he shall inflict upon them physical injuries of any other kind, he shall be exempt from punishment.
These rules shall be applicable, under the same circumstances, to parents with respect to their daughters under eighteen years of age, and their seducer, while the daughters are living with their parents.
Any person who shall promote or facilitate the prostitution of his wife or daughter, or shall otherwise have consented to the infidelity of the other spouse shall not be entitled to the benefits of this article
...banishment or only a prohibition from residing within the radius of 25 kilometers from the actual residence of the accused for a specified length of time. It is not imprisonment.
So, while the punishment is comparatively light -- I assume a "crime in passion" justification here -- it is still a crime, and punished.
The basic premise of the claim, thus, is FALSE.
Regarding the question as asked:
1) Was this ever law in the Philippines? -- Yes.
2) Assuming yes, is this still law in the Philippines? -- Yes, the Revised Penal Code is still in effect today.
I didn't check for 3) and 4), to be honest. I don't think 3) would be a "yes" given the wording of article 247 (I doubt another article will take precedence over one that already cites "exceptional circumstances"), and I consider any answer to 4) to be rather transient and of little value.