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.
