It is very unsecure to store large amount in Android.
Why? And as opposed to what?
I suggest you to export all the addresses created in mobile to your PC but don't export addresses in PC to mobile.
Why?
Store small amount in mobile and bigger in PC.
Why? Malware which targets mobile devices is considerably less common than PC-based malware, and some mobile devices are currently invulnerable to bitcoin-stealing malware (those which cannot yet be easily rooted such as iOS 8.3, most boot-locked android phones running 5.0.2, etc.).