You *CANNOT* use the existing USB ADSL Modem with a Router, it needs to be replaced with a wireless combined "Router & ADSL Modem".
At the moment, the PC connects to the ISP via the USB Modem. When you change to a "Modem/Router", it is the router which must be configured to connect to the ISP, *NOT* any of the computers which are connected to it. They all get their internet access over the Local Area Network from the router.
The settings used in the Modem/Router to connect are essentially the same as those used at present by the USB Modem. There is no phone number involved and, when using a router, there is a permanent connection to the internet unless the router is shut down.