That is what the maker calls a Smartphone Sheath, a thin, flexible condom for your phone that adds a layer of water resistance to your £500 portable little chap. The idea being you suit it up when the likelihood of getting moist increases.
The phone condom comes in three sizes, to accommodate a Galaxy S3, iPhone 4/4S or iPhone 5, so Galaxy Note users may legitimately complain that it's not big enough for them. The user slips it on, plugs the hole in the backside with a reusable sticker and then luxuriates in having a phone that's marginally more protected from licking and spillages than it was before.
£11.99 gets you a packet of, you guessed it, three. [Firebox]