This is a really late reply but I just had to explain haha - though I'm not sure if anyone has already answered this. But anyway, when a man is speaking, "Phom" is far more polite than "chan", and he uses it to generally address a woman who is basically his equal. If he were to say "chan", it can sometimes be to a maid for example, or someone he may consider less than him. A lot of the raeng lakorns have a male address the woman this way - such as Sawan Biang - but this changes later on in the drama and Kawee says "Phom". Btw, I say this speaking in general (it doesn't always make the guy worse or anything if he says "chan"). And having said that, guys may say "chan" when addressing close friends (especially males to males).
Personally in lakorns, I like to hear the pra'ek address the nang'ek with "Phom" (I) and "khun" (you) rather than "chun".
Khun is formal, but also addressed to people you respect. It is the safest word for 'you' if you're a foreigner, and husbands and wives sometimes address each other this way as well. If a man says "Khun" to a woman, he always refers to himself as "Phom", whereas "chun" goes with "ter".
But if it's a casual or close relationship, the name being used for "I" is the best way, and even though it's not exactly formal, it is actually polite. You may say your name for someone who is older than you for example, or to your bf/gf.
I hope that clarified it for you