see - sc.judiciary.gov.ph/jurisprudence/2013/july2013/6664.pdf
"x x x.
Rule 15.03, Canon 15 of the Code of Professional Responsibility provides that: “A lawyer shall not represent conflicting interests except by written consent of all concerned given after a full disclosure of the facts.” Atty. Era thus owed to Samson and his group entire devotion to their genuine interest, and warm zeal in the maintenance and defense of their rights.25 He was expected to exert his best efforts and ability to preserve the clients’ cause, for the unwavering loyalty displayed to his clients likewise served the ends of justice.26
In Hornilla v. Atty. Salunat, 27 the Court discussed the concept of conflict of interest in this wise:
There is conflict of interest when a lawyer represents inconsistent interests of two or more opposing parties. The test is “whether or not in behalf of one client, it is the lawyer’s duty to fight for an issue or claim, but it is his duty to oppose it for the other client. In brief, if he argues for one client, this argument will be opposed by him when he argues for the other client.” This rule covers not only cases in which confidential communications have been confided, but also those in which no confidence has been bestowed or will be used. Also, there is conflict of interests if the acceptance of the new retainer will require the attorney to perform an act which will injuriously affect his first client in any matter in which he represents him and also whether he will be called upon in his new relation to use against his first client any knowledge acquired through their connection. Another test of the inconsistency of interests is whether the acceptance of a new relation will prevent an attorney from the full discharge of his duty of undivided fidelity and loyalty to his client or invite suspicion of unfaithfulness or double dealing in the performance thereof.28
The prohibition against conflict of interest rests on five rationales, rendered as follows:
x x x. First, the law seeks to assure clients that their lawyers will represent them with undivided loyalty. A client is entitled to be represented by a lawyer whom the client can trust. Instilling such confidence is an objective important in itself. x x x.
Second, the prohibition against conflicts of interest seeks to enhance the effectiveness of legal representation. To the extent that a conflict of interest undermines the independence of the lawyer’s professional judgment or inhibits a lawyer from working with appropriate vigor in the
client’s behalf, the client’s expectation of effective representation x x x
could be compromised.
Third, a client has a legal right to have the lawyer safeguard the client’s confidential information xxx. Preventing use of confidential client
information against the interests of the client, either to benefit the lawyer’s personal interest, in aid of some other client, or to foster an assumed public purpose is facilitated through conflicts rules that reduce the opportunity for such abuse.
Fourth, conflicts rules help ensure that lawyers will not exploit clients, such as by inducing a client to make a gift to the lawyer xxx.
Finally, some conflict-of-interest rules protect interests of the legal system in obtaining adequate presentations to tribunals. In the absence of such rules, for example, a lawyer might appear on both sides of the litigation, complicating the process of taking proof and compromise adversary argumentation x x x. 29
The rule prohibiting conflict of interest was fashioned to prevent situations wherein a lawyer would be representing a client whose interest is directly adverse to any of his present or former clients. In the same way, a lawyer may only be allowed to represent a client involving the same or a substantially related matter that is materially adverse to the former client
only if the former client consents to it after consultation.30 The rule is
grounded in the fiduciary obligation of loyalty.31 Throughout the course of a lawyer-client relationship, the lawyer learns all the facts connected with the client's case, including the weak and strong points of the case. Knowledge and information gathered in the course of the relationship must be treated as sacred and guarded with care. It behooves lawyers not only to keep inviolate the client’s confidence, but also to avoid the appearance of treachery and double-dealing, for only then can litigants be encouraged to entrust their secrets to their lawyers, which is paramount in the administration of justice.32 The nature of that relationship is, therefore, one of trust and confidence of the highest degree.33
x x x."
