Short answer. Yes. A lawyer who takes up the defence of the opposing party in the same case, after acting for you or after receiving your confidential information, commits a crime under the Revised Penal Code unless you consented. It is a criminal charge on top of, not instead of, disciplinary proceedings.
What the law says
The same penalty shall be imposed upon an attorney-at-law or any person duly authorized to represent and/or assist a party to a case who, having undertaken the defense of a client or having received confidential information from said client in a case, shall undertake the defense of the opposing party in the same case, without the consent of his first client.
Revised Penal Code, Article 209 — Betrayal Of Trust By A Lawyer. Read the full provision →
The two things the article punishes
The provision covers two distinct wrongs. The first is prejudicing your interests, or revealing secrets you told him in his professional capacity, through a malicious breach of professional duty or through inexcusable negligence or ignorance. The second — the one you are describing — is switching sides: having acted for you, or having received confidential information from you in a case, he then takes up the defence of your opponent in that same case without your consent. Note that the second wrong does not require proof that he actually leaked anything or that you lost. The act of appearing for the other side, in the same case, is the offence.
What the penalty is today
Be careful with older reproductions of the Revised Penal Code, which still print the peso figures set in 1930. The fines throughout the Code were revised by Republic Act No. 10951 (2017), and the current text imposes prisión correccional in its minimum period, or a fine ranging from Forty thousand pesos (₱40,000) to Two hundred thousand pesos (₱200,000), or both. The article also says this is in addition to the proper administrative action — so a criminal case does not replace a complaint to the disciplinary authorities over his licence, and neither one bars the other. Any source quoting much smaller amounts is giving you the pre-2017 version.
Where the provision has limits
Three limits matter in practice. It is confined to the same case — a lawyer who later acts against you in an unrelated matter may face professional consequences, but that situation sits outside this article. Consent is a defence: if you agreed to the arrangement, the switching-sides offence does not arise, which is why written waivers of conflict exist. And the negligence branch requires more than an ordinary mistake or a losing strategy; the text speaks of inexcusable negligence or ignorance. A judgment call that turned out badly is not automatically criminal.
What to do if you suspect this
Preserve the record before you confront anyone: your engagement documents, receipts, messages, and every filing showing who appeared for whom and when. Note the exact dates he acted for you and the date he first appeared for the other side, because the overlap in the same case is the core of the complaint. Terminate the engagement in writing and demand the return of your files. A criminal complaint and a disciplinary complaint follow different routes and different evidence, so have the material assessed by another lawyer before filing either. Nobody can tell you in advance how a particular complaint will be resolved.