This is one of three required pieces for digiscoping with the Impact system. In addition to the phone phone block, you will need a phone adapter and an eyepiece adapter.
The phone block is semi-permanently stuck on to a phone case and serves as a base to align to the phone camera(s). The standard block will work on just about any phone but only allows for alignment to a single lens. The Pro Phone Blocks allow use of both the regular and telephoto lenses. The configuration of lenses determines the shape of the block so the footprint on the phone will vary from block to block.
The setup video here shows how it works in a little more detail.
