We don't have many banner icons here, so it's a good idea.
U could zoom it in a bit.
The bg doesn't really fit.
U could change it, darken it or add some strong shading around the flag, to make it stand out better.
I never recommend black outlines.
Try to use darker tones of the colors that you've chosen.
The details on the flag need work.
The Phoenix can be represented in various ways, from the simplest, stylized, to the most complicated and realistic.
I see that u tried to draw a stylized Phoenix, but it doesn't look quite like a Phoenix, u need to work more on this.
Also, the whole banner needs some shading.
I would be happy to see an update of this flag.