follow the lines on the phone case, there is a harder plastic shell and inside is a softer silicone like piece. You can feel the difference in the material. Just grab the softer section and pull, either the top, bottom, side buttons, through the camera lens cutout.I mean they are stuck together and do not come apart that I can see.
You said “So you can just have the phone in the silicone piece then when needed, just attach the outer part.”.
Show a pic of the the parts not connected and describe how you pulled them apart?.