Part 2:

I do recommend learning English phonology. All the sounds of English are different from those of your native language, so it makes sense to learn (and master) how to move the lips, tongue, etc. to make the exact sounds used by native speakers. The phonotactics is also different — how the sounds influence each other. Plus, you need to master prosodic elements — rhythm, stress, intonation, etc. All this not only makes you sound better, but since the way you speak is the way you expect to hear, your listening comprehension will grow much faster. This should be done before learning thousands of words with poor pronunciation.

Wikipedia article on the basics of English phonology:

University of Iowa web-app for learning English vowels and consonants:

On Youtube, “Rachel’s English” is also good for learning American English pronunciation.

I agree with most of Benny's points (he's clearly had experience with this), except that I am in fact familiar with several books that teach English pronunciation to non-natives -- that is what you need. A teacher specializing in teaching pronunciation to non-natives can also make a huge difference -- the sooner, the better.

EDIT: I accidentally inserted the word "English" before "teach" instead of after.

Yes, but don’t expect it to be that significant.

Part 1: As applied to English, “phonics” refers to associating spelling patterns with pronunciation. For the most part, this is indeed how native speakers learn to read and write English. This is of course after they have already internalized the English phonological system and become proficient in conversational English. I believe it can be worthwhile for ESL learners to take the time to learn the basics of phonics (there are videos on Youtube), but do not expect it to be a great help.

Unfortunately, English spelling just is not that regular — the basic vowel rules only work 70-90% of the time. Sometimes, all the rules in the world won’t help, for example “they’re”, “there”, “their”, or thought, cough, tough, though, through, plough. Or “tear” (ripping or weeping). Even native speakers who know phonics will often learn a word with the wrong pronunciation if they have never heard it spoken. In many cases it doesn’t matter much, since such words are rarely used, or rarely used in the spoken language. If a beginner ESL student were to try this, he or she would be mis-learning basic vocabulary.

I would not recommend that someone who does not already have English speaking and listening skills rely on phonics to learn English by reading. Instead, it would be best to do a lot of listening, especially audio programs designed for learning the language or otherwise at the learner’s level. An advanced learner can try watching TV series. If reading practice is desired, there are always the subtitles and / or transcripts. ESL material should come with books and audio / video material. Eventually, reading will be useful, but try to use material that is at an appropriate level — where you already know 85-95% of the words. The 5-15% that we don’t know are always the most important ones for understanding the story, even though (ironically) they are the least important for us to memorize.

Phonics is for native speakers to learn SPELLING. They learn PRONUNCIATION from their parents.

In Thailand, phonics are also taught to young learners to improve pronunciation. The problems are that,

The notations you use suggest that you mean <em>phonetics</em> rather than phonics. It so happens that phonetics is a rather advanced subject with its unique phoneme notations such as the schwa (ə). This is by definition not very suitable for small children, who struggle with a foreign alphabet anyway.

Phonics is a related but different idea. It uses basic words that children learn early, and then uses their familiar sounds to represent longer words. An example would be to use the o sound in dog to represent the same sound in holiday, and the o sound in go to represent the same sound in below. This is the correct method to use with small children.