There’s bound to be that certain someone that you’d just rather not talk to. But blocking their call may not be the best option, as it could be a co-worker or family member that you’ll want to speak to eventually.
The best choice then is just to send their call directly to voicemail. The process is pretty straightforward. First, find the contact you want. You can open your phone’s dialer app or go directly into the contacts to locate that individual.
Then, touch the Pencil icon or Edit button (this will vary by your contacts app's interface).
Next, click the overflow button (three vertical dots) and check All calls to voicemail. You can change this behavior anytime by repeating the process, and you’ll be able to take their calls again.
Note that some contacts applications included with some phones don't have this option, but it's present in the stock Google contacts app and many others.