Interesting idea but we need more information to be able to understand this project you mentioned mining, is it done with hashing algorithms? That would shorten the life of both the battery and the phone.Anyway good luck team Phoneum.
Well, this coin is different, there is a network behind it and the algorythm altough haven't been disclosed, its ethereum alike. As far as I know, the app doesn't do any harm to your phone nor battery. I've been using it since the first 0.3v release and never done anything bad to my phone. I've been using my phones for mining and they get pretty hot, but with phoneum app, they don't. I have a heater in the bedroom, gets pretty warm and the phones don't those stay cool.
So, don't worry and as for now, everything mined is being produced on a testnet, when the app launches officially, all coins will be burn. Feel free to try it and to keep the app tidy, talk about the errors, crashes and stuff. I don't know much, but I can help.
Keep this going
Regards
GilRH