Wireless connections stops working time to time...

Well with a D-link I used to have the same issues on a multi level condo I was living in the past.
And I can pretty much bet that for you, the connection has not dropped because you moved your cordless phone from the same floor where the router is. And even if you didn't move it, the distance b/w the D-link router and the cordless station has increased or some barrier is in the middle.

Best bet is to get a DECT type cordless phone. Since I switched to a DECT 6.0 type cordless system at home, my D-link issues hardly pop up.