When you answer the phone and don't know who's speaking, what's a polite way of asking, "May I ask who's calling, please?" Thai.language.com says "่ไม่ทราบว่าใครกำลังพูดครับ" but my brain doesn't like the way that translates......'I don't know who's talking". My wife says it's okay to say "ใครพูดครับ". Suggestions?

I think that your wife's suggestion will be ok, polite enough but not excessivelly.

The form you found "่ไม่ทราบว่าใครกำลังพูดครับ" sounds like "(sorry) I didn't recognize who is talking" which it does not sounds that bad to me and maybe

in some way it can sound more polite because it's not a direct question.

No - it's not a question, simply a statement that may or may not lead to the person on the phone identifying themselves. I see nothing wrong with ใครพูดครับ; it's short and polite. I normally use นั่นใครพูดครับ (who is that speaking) which seems to get the desired reply.

If you want to be extra polite, there are variations on this one:

(ไม่ทราบว่า)เรียนสายกับใครอยู่(ครับ/คะ)

The parts in parentheses aren't strictly necessary, but you'd want to have one or more to match the politeness level of เรียนสาย, which is fairly formal, and thus very polite. You might translate it as "May I ask to whom I am speaking?" which sounds rather formal in English, too, at least to me.

i often say .. ขอโทษนะคะ นี่ใครพูดอยู่คะ ?

i often say .. ขอโทษนะคะ นี่ใครพูดอยู่คะ ?

Thanks for all the replies. Thithi's fits my style best.

By the way......what's with ซวย ส่วย ส้วย ซ๊วย "สวย"

i often say .. ขอโทษนะคะ นี่ใครพูดอยู่คะ ?

Thanks for all the replies. Thithi's fits my style best.

By the way......what's with ซวย ส่วย ส้วย ซ๊วย "สวย"

hehehe it just the word สวย in the 5 tones