Article 190. Legal or intestate succession to the estate of the adopted shall be governed by the following rules:

(1) Legitimate and illegitimate children and descendants and the surviving spouse of the adopted shall inherit from the adopted, in accordance with the ordinary rules of legal or intestate succession;(2) When the parents, legitimate or illegitimate, or the legitimate ascendants of the adopted concur with the adopter, they shall divide the entire estate, one-half to be inherited by the parents or ascendants and the other half, by the adopters;

(3) When the surviving spouse or the illegitimate children of the adopted concur with the adopters, they shall divide the entire estate into equal shares, one-half to be inherited by the spouse or the illegitimate children of the adopted and the other half, by the adopters.

(4) When the adopters concur with the illegitimate children and the surviving spouse of the adopted, they shall divide the entire estate into equal shares, one-third to be inherited by the illegitimate children, one-third by the surviving spouse, and one-third by the adopters;

(5) When only the adopters survive, they shall inherit the entire estate; and

(6) When only collateral blood relatives of the adopted survive, then the ordinary rules of legal or intestate succession shall apply. (39(4)a, PD 603)

The Article applies only in legal or intestate succession.

An example of paragraph 1 is:

An adopted child died intestate survived by his wife and five (5) legitimate children. If the estate is P12 million, how should it be distributed?

The wife shall have the same right as each of the 5 legitimate children. Hence, the estate will be divided into 6 equal shares with each child inheriting P2 million. The wife shall also inherit P2 million.

An example of paragraph 2 is:

X and Y are the parents by nature of Z, who is eventually adopted by A. If Z dies with an intestate estate of P18 million, how will the estate be divided?

Half will go to the legitimate parents so X and Y will get a total of P9 million while A will inherit P9 million.

What is the difference between paragraph 3 and 4?

In par. 3, the word OR is used (illegitimate OR surviving spouse); in paragraph 4, AND is the word used. 

In par. 3, the estate is divided into 2 parts; in par. 4, 3 parts are involved.

In paragraph 5, if the only survivors are the adopters, they get the entire estate. Clearly, all indications point out that the adoption shall exclude collateral relatives of the adopted.

What if only the collateral relatives survive?

In paragraph 6, the rules are set forth in Articles 1004-1010 of the Civil Code.

References:
Civil Code of the Phils. Annotated 16th Edition by Edgardo Paras
Family Code of the Phils. 2017th Edition by Ed Vincent S. Albano