So, there is too way to do it.
If you go outside and you want a clean sound, find a spot where there is at least one wall to cut off the wind, and external sound. It's also a matter of luck, some days, it's just not windy and there is no sound. Try to keep the phone that you record from not further than 2 meter away from you, or the sound quality won't be as good.
If you have a laptop, the other solution is too record video on one side, audio on the otherside with ambient mic, and then mix them in post prod.
At last, if you want the perfect clean sound, I would suggest to:
- Record the audio first
- Lip Sync in a video, pretending to play?
That allows you to have 2 or 3 camera angles, a clean sound, and it's more engaging for the audience. You can also add backing vocals!