Are you talking about teaching phonetic symbols or teaching with the help of phonetic sound interpretations using Portuguese to mimic English sounds?
You don't need to teach a phonetic code specifically. What you're trying to do is to get a learner to reproduce accurately the English sounds he/she hears.
You can teach orally, for example, "man-men", "woman-women" with pictures, and no reference to written English. The only guide to pronunciation would be your voice, or a recording.
At another stage, you could introduce the English written forms, after the person already knows the meanings and can say the words, to link the spoken forms with the written forms.
If you follow some such process systematically, you can minimize the need for a phonetic code, and minimize interference from Portuguese.
Basically, you need an approach to listening-speaking-reading-writing, allied with visual and listening aids. Phonetic symbols are simply another tool you can make use of to carry out a method of teaching and learning.