Unchecking the "show notifications" for the Phone app
Since you've root access, you can easily allow or ignore the notifications of any app. 


Install a file manager having root explorer feature such as ES File Explorer or MiXplorer.
Go to /data/system and open notification-policy.xml.
Add &lt;package name"PKG_NAME" /&gt; between &lt;blocked-packages&gt; and &lt;/blocked-packages&gt;, such as:

(Click image to enlarge)



Replace PKG_NAME with the package name of the app whose notifications you don't want to see. See View app&#39;s full package name?
Save the file and reboot the device. The "Show notifications" checkbox would now be seen unticked.





There's also an alternative approach which didn't work for me. You may give it a try though. Find it here.