Go to Settings -> Apps & Notifications -> Advanced -> Permission Manager -> Telephone
Deny all apps for this permission only allowed Phone app.
After this restart and check your phone will work again as it was working before.
There is some issue with telephone permission when given to other apps. So whenever any apps ask for permission deny it or if it dont work without permission then allow it for a while till you want the app to work and then deny/disallow telephone permission for that app.
Whenever you see problem go to same option as mentioned above you will see some other app too have telephone permission which you have to remove and then it will start working again.