How to make a cover like this?

I'm gonna make a cover of a song on youtube. The problem is i only have my iphone to record which means there's a lot of side noise and i don't know how to get the background of the song when i'm playing. So how can i stop background noises (crackling etc) and get the background noise? People on youtube do it crystal clear how do they do that?

Usually the people on youtube that have their audio "crystal clear" have a better microphone.
I'm going to suggest two things.
1. You could go out and buy a better mic.
2. You could deal with the noise. Maybe going into a quiet room will help.