bigger on the inside than outside

On the science fiction TV show Dr Who, the Doctor travels throught time and space in  a Tardis. On the outside it looks like a  20th century British Police box, but walk on the inside and you enter a massive pocket dimension.

A smart phone is a tardis like object  On the outside it looks like  an object a bit bigger than your hand,

but on the inside this Tardis holds  more information then is contained in   10,000 libraries of congress.