The exchange I use to trade altcoins from my phone is Binance. You can register here and download the app in the google play store
Binance: https://www.binance.com/?ref=10808506
BINANCE ON IOS: https://www.binance.com/ios-install.html
BINANCE ON GOOGLE PLAY: https://play.google.com/store/apps/details?id=com.binance.dev
Referall CODE: 10808506
KUCOIN: https://www.kucoin.com/#/?r=1dHMP
REFERALL CODE: 1dHMP