p2 collision groups

[Phaser]

http://phaser.io/examples/v2/p2-physics/collision-groups

The example given uses the collides method to handle the contact. The problem is it only fires on first contact and so if you remain pressed against the object it won't continually fire... what is the best way/proper way in Phaser P2 to handle collision? Collides seems to only handle begin contact how about the end contact? Or repeating the collision every so many seconds? 

I'm only trying to understand the proper way to use the P2 physics system as it is and I don't want to reinvent the wheel because I don't understand the tools I already have.