I must say that in my experience both in my past life in Greece and my much wider experience over the last few decades speaking to Greek-Americans or Greek expatriates the preferred translation for this not what are you doing but rather what are you making or what are you fixing or preparing or constructing depending on what the specific situation is.
But to hear this in isolation I would never say what are you doing as a translation for this. I could understand the situation where it would arise. To me it seems like a slang expression. Here again of course I am far removed from everyday usage of Greek has spoken in Greece.
My comments are only from my perspective.
I think "making" or "producing" should be the right translation for "φτιάχνω".. I am taking Greek lessons from a native Greek professor since 1.5 years. We are using φτιάχνω also for cooking, for actually preparing the dish in the kitchen. We have never used this verb to say "what are you doing?" Maybe the correct translation for this sentence should be "what are you making ?"
While "doing" is a general word to define any action, I'm sure we can find an exact English word corresponding to φτιάχνω here - like "fixing" or "preparing"...
Or "making". I would like to add that when you say "τι φτιάχνεις;" speaking informally, you can mean "how you doin'?"
" What are you preparing" should I think be added. In a previous sentence (I think it was " He is preparing soup") "prepare" was accepted as the translation of φτιάχνω.
The form of ποιέω is not used in modern greek. Ποιώ is there but sounds archaic when used on its own and its usage is mostly about "creation" and not about "preparing meals". Ποιώ is used in everyday life as a second component of compound words, for example Χρησιμοποιώ =use, μεγαλοποιώ = magnify, exaggerate etc. So you can't really say Ποιώ for preparing food. Φτιάχνω is the verb used on its place in modern greek.
The answer "What are you cooking?" was marked as wrong. Is this because this is a generic expression? Thank you.
How would you pronounce this? I seem to be having trouble especially with the "φτ" and "xv" parts.