"Ik zal je overmorgen bellen."
Translation:I will call you the day after tomorrow.
I submitted the same response and was gobsmacked that 'phone' is not acceptable. I duly reported it, but from what you said it looks as if a correction is unlikely. It's weird, because I am positive that there have been other questions where 'phone' was accepted in the answer. It's a UK English-US English disconnect.