I can't hear you.clearly.
我听不太清楚。
I can hardly hear you.
我听不太见。/我几乎听不见。
Say that again,please?
请再说一次。
Could you speak up a little,please?
可以请你说大声一点吗？
Does Mark Wyatt work there?
Mark Wyatt 在这里上班吗？
This line is terrible.
电话线路很差。
The line is dead.
电话线路坏了。
Could you spell that for me please?
可以请你拼给我听吗？
Have I got it right?
我说的对吗？
Got it?
好了吗？(听懂了吗？)