<?php

$regexp         = '/^(\\s*([+]\\s*7|8))(\\W*\\d){10}$/';
$regSymbolClean = '/\\W/';
$regCodeClean   = '/^(7)/';

$correctNumbers = [ 
  '84951234567',  '+74951234567', '8-495-1-234-567', 
  ' 8 (8122) 56-56-56', '8-911-1234567', '8 (911) 12 345 67', 
  '8-911 12 345 67', '8 (911) - 123 - 45 - 67', '+ 7 999 123 4567', 
  '8 ( 999 ) 1234567', '8 999 123 4567'
];

$match          = [];

foreach ($correctNumbers as $key) {
		 preg_match($regexp, $key, $match);
		 $сleanNumber = preg_replace ($regSymbolClean, "", $match[0]);
		 $standNumber = preg_replace ($regCodeClean, "8", $сleanNumber);
		 echo "Стандартный номер {$standNumber}\n";
}