请在课堂上把手机关掉。

Qǐng zài kètáng shàng bǎ shǒujī guān diào.

Please turn off your phone in class.

有的问题在课堂上没听懂，我下课再问老师。

Yǒu de wèntí zài kètáng shàng méi tīngdǒng, wǒ xiàkè zài wèn lǎoshī.

Some questions I didn't understand in class, so I will ask the teacher after class.

课堂上不要一直看手机，要认真听讲。

Kètáng shàng búyào yìzhí kàn shǒujī, yào rènzhēn tīngjiǎng.

Don't keep looking at your phone in class; you need to listen carefully.