If the iPhone was actually Apple trying to make the "best phone ever", wouldn't Phone.app have a richer feature set?
Playback stops if you navigate away from the open table-cell
If you are trying to listen to a voicemail and do anything else (like contact management or take notes), playback will stop when you navigate away from the current view or the app itself.
"Recent" visual label is over-used and ineffective.
Example: contact with many numbers
Example: not used in "Favorites" tab. (A grey star is shown, but this view assumes that favorites in a contact have a unique label. For example, if you have two favorite "mobile" numbers for someone, you cannot tell which number is in the favorite you are viewing.
Example: Missed does not use "recent", but the "all" does. (It uses red colored text as "missed".)