Qǐngwèn nín shì nǎ wèi? Wǒ méi tīng qīng nín de míngzi.
May I ask who you are? I didn't catch your name.
Tips
register
Polite phone-answering formula. Three layers of politeness stack: 请问 ('may I ask'), the honorific 您 (vs. 你), and the measure word 位 (vs. 个) for the person. Use this when answering a call from an unknown number.
mistakes
Don't say 你是谁? on the phone — that comes across as blunt and almost suspicious ('who the hell are you?'). The full polite form 请问您是哪位? is the safe default.
