Can't directly. I just bought a cheap used iPod on eBay because I like my handlebar controls and didn't want to use phone.
You can use a 30 pin to headphone jack adapter and attach that to any media player. Several cheap mp3 player options that are not iPods. This does NOT work with handlebar controls other than volume.
Other option is the Bluetooth adapters that you can pair with phone and get basic control next track, previous track, but no information in the bike display.
I did see some old posting on other forum when I was researching options about an adapter that is $200+ that will get track information off a phone.
I have the cheap Bluetooth adapter but the iPod been working great. Does skip occasionally once a day but that's my fault for using the hard drive version I didn't know the difference until after buying.