I want remove my voice [and keep background noise]

The blue line doesn't actually mean anything in this context. If you have a stereo recording and a mono voice in a single position in the stereo field, then you may be able to at least reduce the level of the voice using the Center Channel Extractor. I doubt very much whether it will be anything like perfect though, as generally when you make a recording like this, you end up moving the phone around, and that means that the spatial extraction point would need to move with it - and that's really difficult to do. The only thing you really have going for you is that it's outside, so you won't end up with ghostly echos, which is what tends to happen if you try this with an indoor recording.

But I'm afraid that the chances of getting a good result are very slender.