<?php
 
$rawPhone = "моб. 8(123) 123-4 5 6-7 без выходных";
$regExp = '/(8|\\+7)([^0-9]*[0-9][^0-9]*[0-9][^0-9]*[0-9][^0-9]*)([^0-9]*[0-9][^0-9]*[0-9][^0-9]*[0-9][^0-9]*[0-9][^0-9]*[0-9][^0-9]*[0-9][^0-9]*[0-9])/';
$matches = array();
preg_match_all($regExp, $rawPhone, $matches);
 
if (empty($matches)) {
    die("Номер телефона не обнаружен");
}
 
$cleanPhone = "8{$matches[2][0]}{$matches[3][0]}";
 
$regExpNums = '/[^0-9]/';
$properPhone = preg_replace($regExpNums, "", $cleanPhone);
echo $properPhone;

PD9waHAKCiRyYXdQaG9uZSA9ICLQvNC+0LEuIDgoMTIzKSAxMjMtNCA1IDYtNyDQsdC10Lcg0LLRi9GF0L7QtNC90YvRhSI7CiRyZWdFeHAgPSAnLyg4fFxcKzcpKFteMC05XSpbMC05XVteMC05XSpbMC05XVteMC05XSpbMC05XVteMC05XSopKFteMC05XSpbMC05XVteMC05XSpbMC05XVteMC05XSpbMC05XVteMC05XSpbMC05XVteMC05XSpbMC05XVteMC05XSpbMC05XVteMC05XSpbMC05XSkvJzsKJG1hdGNoZXMgPSBhcnJheSgpOwpwcmVnX21hdGNoX2FsbCgkcmVnRXhwLCAkcmF3UGhvbmUsICRtYXRjaGVzKTsKCmlmIChlbXB0eSgkbWF0Y2hlcykpIHsKICAgIGRpZSgi0J3QvtC80LXRgCDRgtC10LvQtdGE0L7QvdCwINC90LUg0L7QsdC90LDRgNGD0LbQtdC9Iik7Cn0KCiRjbGVhblBob25lID0gIjh7JG1hdGNoZXNbMl1bMF19eyRtYXRjaGVzWzNdWzBdfSI7CgokcmVnRXhwTnVtcyA9ICcvW14wLTldLyc7CiRwcm9wZXJQaG9uZSA9IHByZWdfcmVwbGFjZSgkcmVnRXhwTnVtcywgIiIsICRjbGVhblBob25lKTsKZWNobyAkcHJvcGVyUGhvbmU7