I went for an interview on last month. Everything went smoothly....

Then the company called me up and we further chatted on job requirement, my expectations, their expectations, ect for an hour. Then the in-charge offered me the job verbally via phone. He suggested he will draw up a offer letter for me to review the salary package. That was one week ago...
Now, no news from them.
Should I write to follow up with them......I know I should do that.
How should I phrase it?
Has anyone ever have a company offering the job and later they redraw the whole offer?