Anybody that knows anything about phone tech/viruses?

So I'd given my phone to a colleuege to check a file on Google docs. They held my phone and fiddled with it. They mostly help it with the back of the phone showing towards me from the glimpses I saw there was a green rectangle where the keypad should be and a few pixeallated dots I think red/brown in color. I didn't question them because I wasn't sure if that was a glitch or if something is up with my phone. I'm not on good terms with them so it'd help to know...