To disable the notification for missed calls on the Yealink phones (both the flashing red light and the pop up text) you need to change a setting on the phone itself. This article explains how to disable this notification if you do not require it on the extensions in your queue.
You need the IP address of the phone you wish to change, if you do not know the phones IP address you can press the OK button when the phone is idle and the IPv4 address is displayed, note this down.
From a web browser on the same network, enter that IP address as the URL to get to the web based administration for the phone. The default username and password is admin for both the username and password. If the handset has been purchased via VoIPLine then the details would have been emailed during the order process.
Once logged into the phone click on the Account tab at the top of the page, and then the Basic setting on the left hand side of the page to bring up the settings for Account 1. Changed the Missed Call Log Option to disabled. Then click the Confirm button to apply the changes, see screenshot below.
You will now no longer have a red light notification or the text pop up on your screen to advise about missed calls for that SIP device.