to talk to someone again, usually on the phone, in order to give them some information or because you were not able to speak to them before

I'll get back to you later with those figures. 晚些时候我会给你回电话，告诉你那些数字。

to start doing or talking about something again

Anyway, I'd better get back to work. 不管怎么说，我最好还是继续工作吧。