I am not sure that 'safe' and 'android' should even be used in the same sentence 
Agree. When you see your family photos uploaded to Google+ Circles without your knowledge or approval, you soon realize you have no control of any data or security on the device. Or when you realize you can download an app remotly to a stolen phone to track it's location and even hear what the thief is saying and take his photo.
So how would you use btc at a physical shop like a restaurant?
Sorry, I was just agreeing with the previous poster and hinting that the NSA/Government could probably reach into you phone any time they like.
Sure there's are apps to do that, this is probably the safest one as it remains decentralized and don't host your coins at a 3rd party: https://play.google.com/store/apps/details?id=de.schildbach.wallet