For those asking what a VPN is for, This entirely depends on how security minded you are.
At the most basic level all a VPN does is encrypts all the data from your phone so your Internet service provider ( ISP ), or anyone between your device and your ISP cant see what your looking at.
Normal flow of info as an over view.
Your device -> Modem ( if on wifi ) -> ISP, Your ISP goes the website and gets the data to return to you ( the HTML from the website etc ).
with a VPN.
Your device -> your Modem ( if on wifi ) -> ISP -> VPN Provider which then goes to the data and return it.
So, With a VPN, if your ISP looked at what you were looking at ( for example to see if you were downloading movies etc ), all they would see is the VPN provider and none of the other website data your looking at ( so no idea if you have been downloading movies etc ).
For those using a free VPN. All you have done is shift who knows what your looking at from the ISP to the VPN Provider. the VPN will be selling all this on to make money and will be far less secure than not bothering at all as ISP's have laws to follow that the VPN provider wont.
If your going to get a VPN, pay for one. and if your really security minded. pay for a No logging VPN so there's no evidence to trawl through if there are any requests from any governments/agencies.