I would say that if you are getting an ipod classic, it is better as a music player.
- smaller foot print than a phone
- up to 160gb in your palms
- battery life is still better than a phone (40 hours of playback time, can last up to a week)
- this might be a personal preference but I prefer a clickable button over a full touch screen. Clickable button means you can stop or skip to the next song without having to look at the screen, so very useful when you have your ipod in your pocket and you can just press next without having to ever take it out. Also, if you have your ipod on an arm band when you are running, you can easily press next without having to look for a button on screen since your fingers can feel the button themselves. This is why I still have my ipod as well as my phone as a music player: for use in gyms, it is much better.
This might also be trivial, but I also find that it is better to have less function at times. When I try to get some work done, I put my phone away and just use my ipod classic. And since it can't do anything except for playing songs, I just cannot get distracted, whereas if I had to take out my phone to play songs, I would have to check it every 10 mins.
Again if any of my reasoning applies to you, then thats great. Otherwise, the phone could work for you too.