get retrieved value of database as single input

$user = DB::table('users')->where('name', 'John')->first()->pluck("phonenumber");

This code gives error as Call to undefined method stdClass::pluck()

What version of Laravel are you using? In Laravel 5.1 pluck() was renamed to value().

// 5.0 and earlier
$userPhoneNumber = DB::table('users')->where('name', 'John')->pluck('phonenumber');

// 5.1 onwards
$userPhoneNumber = DB::table('users')->where('name', 'John')->value('phonenumber');

https://laravel.com/docs/5.1/upgrade

if you use pluck as part of a query then you will get an array of results

using first will return the first of possibly many matches and the you can access the attributes directly without using pluck

$user = DB::table('users')->where('name', 'John')->first()->phonenumber;