This has to be the most fun I've ever had making a costume and it was so simple! Obviously, it is a mashup of Doctor Who and the SNL sketch "Dick in a Box."
Step 1 - Cut a hole in the (phone)box.
Step 2 - Put your junk in that (phone)box.
Step 3 - Have her open the (phone)box. And that's the way you do it.
I already had the 11th Doctor costume so the biggest thing I had to do was assemble the perfect size box and wrap it to look like a TARDIS gift box. Then I constructed the special surprise on the inside of the box. Yes, it is bigger on the inside. I bought sunglasses, gold chain and skeezy facial to complete the look.