I'm thinking of: dialer app, SMS app, contacts app, settings app.
The problem seems to be that OEMs mark apps as non-removable when they don't fit that category. And even google does this. [eg. Looking on my phone I was not able to remove Google News, only "disable" it.]
And also on Android, you can install multiple dialers, multiple SMS apps, etc., so maybe you should be able to get rid of the stock one if you have a replacement.