Hi sven, so if I understand you correctly you want to make the hole that the iPhone sits in.

That hole is not just a simple hole with straight side walls, which is what you will get with things like extrusion, it is more molded to the same shape of the iPhone itself.

So that also means that you will have to create an iPhone like solid, and then use that iPhone shaped solid as the cutting object in a Boolean difference operation to cut the bottom block.

That would go something like this - model the shape of the iPhone:



Position that shape in relation to your base like this:




Now select the base, run Construct > Boolean > Difference, and use the phone part as the cutting object, that will give this kind of result:




I guess there may be some other kind of cut in addition to that, maybe something sticking forwards like this:




But anyway if you want to get a hole that has a kind of molded shape to it, you will usually need to model that shape as a separate part, then use it as the cutting object in a boolean operation, that will cut the base object and leave the imprint of the shape on it.

- Michael

EDIT: Danny beat me to it! Thanks Danny!