If you get unwanted phone calls from people that you may want to block it really is very easy.
On an Android phone look for the more or the dots in the top right hand corner of the screen and you will be presented with the option to block.
On an iPhone
Go to your list of recent callers .(open the Phone app, then hit the Recents tab at the bottom). Click the ‘i’ symbol next to the number you want to block, scroll down and tap Block this Caller, then confirm your decision.