Nǐ wèishénme bù jiē diànhuà？  

你为什么不接电话？

Why didn't you get the phone?

Notes:

你(nǐ): you

为什么(wèishénme): why

不(bù): not

接电话(jiē diànhuà): to answer the phone

Example:

A：你为什么不接电话？

     Nǐ wèishénme bù jiē diànhuà？

     Why didn't you get the phone?

B：我没听见。

     Wǒ méi tīnɡjiàn.

     I didn't hear it.