Well my iPod touch 4g which isn't as good as your phone. but seems to be along the same family line.
I turned on WebGL
You used a TileBackground, but those should always be power of 2(1,2,8,16,32,64,128,256,512,1023,2048) and not any other. So I changed that to 256. However since your background is only of 1 colour. I made the layout BG colour to that of the image colour. I turned off clear background. Also I'm not 100% sure on this. but I don't believe CocoonJS supports TiledBackground very well and using that will cause slow down.
You On Touch and Every 1 second is improper. and I fixed that up too.
Prior the game ran at 30fps.
Before changes and WebGL turned on ran at 60fps
For me the game runs at 60fps.
The explosion animation kills performance. And here is why.
There are a total of 6 frames in your animation. However your forcing an animation rate of 15/19(bullet1/2) was too high. What is happening is that C2 is trying to cycle through the animations faster than you have animations. So this is causing your animation to get into very large loops which is causing a massive performance hit. This really shouldn't happen at all. But it is being wierd. For some reason a speed rate higher than your frames seems to create a minor slow down. wierd.
I toned this down to just 3 fps for a test and the speed ran fine. Of course you want the explosion to be more than 3fps. So do was you need. But be careful not make it to high.