$re = '/(?>\G(?!^)|^(?:.*?[^\p{P}\h\d\n])?[\p{P}\h]*+1?(?=(?1){10}(?!(?1))))((\d)[\p{P}\h]*+)(?:[^\d\n].*)?/m';
$str = ' +18005551212
8005551213
18005551214
(800)555-1215
800.555.1216
(800) 555-1217
800 555 12 18
stuff before +18005551221 stuff after
stuff before 8005551222 stuff after
stuff before 18005551223 stuff after
stuff before (800)555-1224 stuff after
stuff before 800.555.1225 stuff after
stuff before (800) 555-1226 stuff after
stuff before 800 555 12 27 stuff after
5551212';
$subst = "$2";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php