<?php
 
error_reporting(-1);
 
$text = "8-(911)-506 56 88";
$unnecessarySymbols = array("-", "(", ")", "+", " ", "|");
$cleanNumbers = str_replace($unnecessarySymbols, "", "$text");
$length = mb_strlen($cleanNumbers);
$regexp = '/^8([0-9]{3})([0-9]{7})$/u';
if ($length != 11) {
    echo "Номер телефона должен состоять только из 11 цифр!\n";
    } elseif (preg_match($regexp, $cleanNumbers)) {
        echo "Телефон введён правильно.\n";
    } 
?>

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