This means your phone has not picked up a network connection from your router.
Please disconnect the network cable from the back of your desk phone - leave this unplugged for 5 minutes before plugging back in again which should then resolve this issue.
If not please try re-booting your router and/or switch (if using a switch to connect to your router) as well as disconnect the network cable from the phone - re-boot and re-connect your phone.
Your phone will then display the message 'Network Connecting' as the phone connects to your router - after a few minutes the phone should then receive a network connection from your router.