The standard controls for mobile devices involve gestures.
Depending on what mobile device you're using, you may or may not be able to use multitouch...

Android lets you do this easily, and it has a solid base in Processing.
What type of phone are you developing for?

There may be some libraries to help you on the Processing Libraries Page...

In other words, you are using Android Processing...
I suppose it would have helped to notice the forum it was in...

Perhaps look at this post:
https://forum.processing.org/topic/a-basic-multi-touch-gesture-demo-for-android

You can use the double-tap and pinch, perhaps?