Both the iPhone apps and the modern version of iTunes are an utter, over-designed mess. It felt like the core programming functionality was there, until some UX designer got a hold of the front end of those apps and decided to fubar it beyond recognition.
There is _Literally_ no way to just look at all music on your iPhone. You have to have it in playlists or add the songs you want to a playlist, or just shuffle all songs.
*Edit: No way to look at all iPhone songs while not using iTunes with your iPhone plugged into your PC.