I don't see what's confusing about the app, both on macOS an iOS. You get a preview of your face, the last contacts you called and a green "New call" button.
To me this is simple to the point of being excessively simple, especially with the "missed calls" being in a 16x16 click target dropdown.
It looks like they optimized for "calls from grandma" mode.
You don't see what's confusing, and then you proceed to mention something confusing. If a basic-skills user can't find "missed calls", that's confusing!
The call actually does appear in the Recents list in red, with the time of call, it just doesn't say "missed" explicitly. This matches how the Phone app has looked for the past 20 years.
The "missed calls" list I mentioned would be more of a filter, which is indeed annoying but not fundamental.
To me this is simple to the point of being excessively simple, especially with the "missed calls" being in a 16x16 click target dropdown.
It looks like they optimized for "calls from grandma" mode.