Everything I say here applies also to the use of your cell phone because it is digital recording: Mic position is crucial. Be sure to give your recordings a good listening because you can get pops and rumbles and whatnot due to the mic vibrating. Much of this can be removed in a program like Audacity, but it's still good to get a good angle on the mic that reduces this noise at the start. The trick is to back off a little because you can raise the volume in the processing. It is not like working with analog recorders. With those you want to get up close and hot on the mic with the level just touching into the red. With digital you back off and don't get in too close to the subject. Getting too close is where you will get noise. You want to pick up the sound without allowing him to cause the mic to vibrate against it's enclosing casement. The idea is to get the mic diaphragm to vibrate without vibration on the outer casement. If you go outside, the wind can sweep across the casement and get that part vibrating. You need to shield the mic.

You might want to ask a friend who has experience to accompany you.
Also, with a digital recorder, you and your subject can experiment with overdubbing.