Waterproof phone holder - kinda says what it needs to huh?
 
However these are more versatile than that, carry your bank cards in it, a single house key, some spare coins (remember those !!).
 
Great for when you are on the water, at a festival or just generally needing your pockets or hands free. They can be hung round your neck or have a strap that can be used around your arm for ease of movement.
 
For those that carry their phones remember to put them in upside down so that you can then use them more efficiently on the go - works best without any casing but you will get the feel when it arrives.
 
Also, as a side note, if you do go out on the water with these then make sure you have downloaded the app What3Words as should you need to give directions then this 3 point reference marks an exact location for any emergency services to locate.