D-Link DPH-50U Quick Install Manual page 9

Connect a telephone cable between the DPH-50U line jack
and a wall jack as shown below. Note that this is only required
for making regular phone calls or for forwarding Skype calls
to your mobile (or other off-site) phone or for toll bypass
applications.
You final configuration should resemble the following.
D-Link DPH-50U Quick Install Guide 9