They almost have the ability in your router with the parental controls....but missing url restriction to only certain mac.
So it will be harder. You are going to have to use a IP filter to get it.
First problem is making sure the phone always gets assigned the same ip. In the DHCP screen you need to add a entry to map the mac to a particular ip.
Now if you go to the ip filter screens you need to create a outbound ip filter, change the default to allowed, then add a filter with the source address you specified in the dhcp and the destination address of www.facebook.com. You can leave the port numbers blank.
The problem is www.facebook.com has many different IP. In general it will not change at your house but it might if...