u can just use the core desktop wallet to stake, but you'll need to leave ur computer on all the time. your best bet is to just get a cheap digital ocean vps and install nxt on it and stake with it 24/7. install is very very easy. then u can login to ur nxt server from ur browser. the current 1.5.15 version is more or less mobile functional to do basic stuff, but its still being worked on.
you can connect to any of the 2000+ nxt nodes out there to test it out on your mobile:
http://nxtpeers.com -- remove the /test in the url to get to the wallet when clicking on any of those nodes.
get you wallet from
www.nxt.org