A shielded cable might help but a better solution would be to get a separate Modem and Router or to supplement the existing Hub with a small switch and Wireless Access point.

Rather than run a shielded RJ11 (actually shielded 2 pair Cat5e with RJ11 connectors), run a full Cat5e cable between the two locations. Install a standard back box at each end and fit RJ45 sockets. Ethernet signals are a lot less prone to noise than the basic DSL signal.

Then EITHER.

Install a modem at the point of entry and the Ethernet output from the modem connects to the RJ45 socket with a short patch lead. At the other end another patch lead connects the RJ45 to the router.

OR

Install your existing hub at the point of entry - you will have wireless there and several Ethernet ports. Connect one of those ports to the RJ45 socket and at the remote end, connect the RJ45 to a small 4 or 8 port switch and the WAP to the switch.