How to show a field in views only when a checkbox is ticked?
You can do this with Views out of the box. No need for Views PHP here.


Add your boolean field in Views. (This assumes the default boolean set up, i.e. 0 for not checked and 1 for checked.)
Use the Key formatter - this isn't obvious, but I couldn't get it to work without this.
Select REWRITE RESULTS and put the description you want in there. This can include tokens so you can grab material from other fields in the node if that's what you need.
On NO RESULTS BEHAVIOR check all the boxes (Count the number 0 as empty, Hide if empty, Hide rewriting if empty)