I would guess the focus setting might be on continuous mode but check your settings here.. http://www.kenrockwell.com/nikon/d90/af-settings.htm

The usual thing to do is leave your phone in a bag of rice for a couple of days which should absorb all the moisture. Then try again.

Have you downloaded the latest version of Android? I always seen to get problems with my phone when an upgrade is due and it's probably because there is an app which can only run properly on the latest version, so is crashing your phone.