Well, it all depends on the iphone case. A lot are just a plastic case with a stick on sublimatable aluminium panel that you press in a swing arm or clamshell press. Some however you actually press directly onto the case which require a 'puck' be inserted into the blank and then you press directly to the case. There are also now vinyl sheets that you press and then peel and stick onto the phone section by section.

The common factor is however the need for a press and if the item is thick you will be better off with a swing arm press than a clamshell due to issues they exhibit with uneven pressure on thicker items.

Anyway Welcome to the forum.