Question

Why the following regex: $regex = '/\b(V|E)?\d{1,2}? ?\d{3} ?\d{3}\b/i';
does not match all the input below

I did think that the this (V|E)?\d{1,2}? ? would made optional the letters, the first one or two number and the first space

INPUT

<?php

$sms = array(
    'test test test 11 111 111 test test test',
    'test test test 1 111 111 test test test',
    'test test test 111 111 test test test', // does not match
    'test test test test test test 11111111',
    'test test test 1111111 test test test',
    'test test test 111111 test test test', // does not match
    'test test test E11 111 111 test test test',
    'test test test V1 111 111 test test test',
    'test test test V111 111 test test test', // does not match
    'test test test V11111111 test test test',
    'test test test V1111111 test test test',
    'test test test E111111 test test test', // does not match
    'test test test V 11 111 111 test test test',
    'test test test V 1 111 111 test test test',
    'test test test E 111 111 test test test', // does not match
    'test test test V 11111111 test test test',
    'test test test V 1111111 test test test',
    'test test test V 111111 test test test', //does not match
    'test test test V11 111 111 test test test',
    'test test test V1 111 111 test test test',
    'test test test E111 111 test test test', //does not match
    'test test test V11111111 test test test',
    'V1111111 test test test  test test test',
    'test test test V111111 test test test', // does not match
);

$regex = '/\b(V|E)?\d{1,2}? ?\d{3} ?\d{3}\b/i';
$noMatches = 0;
$index = 0;
foreach($sms as $v) {
    $match = preg_match($regex, $v, $matches);



    if($match) {
        //print_r($matches);
        //echo "$v match!\n";
        //$matches++;
    }
    else {
        echo "$index - $v does NOT match!\n";
        $noMatches++;
    }
    $index++;
}
$total = count($sms);
echo "\n\nTotal: $total\nNo Matches: $noMatches\n";

OUTPUT

$ php test-regex.php 
2 - test test test 111 111 test test test does NOT match!
5 - test test test 111111 test test test does NOT match!
8 - test test test V111 111 test test test does NOT match!
11 - test test test E111111 test test test does NOT match!
14 - test test test E 111 111 test test test does NOT match!
17 - test test test V 111111 test test test does NOT match!
20 - test test test E111 111 test test test does NOT match!
23 - test test test V111111 test test test does NOT match!


Total: 24
No Matches: 8

EDIT:

Using mario suggestion the regex is now $regex = '/\b(V|E)?\d{0,2} ?\d{3} ?\d{3}\b/i';,
why in some cases, this regex does not capture the letter V or E

$output = array(
    'test test test E11 111 111 test test test' => 'E11 111 111',
    'test test test V1 111 111 test test test' => 'V1 111 111',
    'test test test V111 111 test test test' => 'V111 111',
    'test test test V11111111 test test test' => 'V11111111',
    'test test test V1111111 test test test' => 'V1111111',
    'test test test E111111 test test test' => 'E111111',
    'test test test V 11 111 111 test test test' => '11 111 111', // Missing Letter
    'test test test V 1 111 111 test test test' => '1 111 111', // Missing Leter
    'test test test E 111 111 test test test' => 'E 111 111',
    'test test test V 11111111 test test test' => '11111111', // Missing Letter
    'test test test V 1111111 test test test' => '1111111', // Missing Letter
    'test test test V 111111 test test test' => 'V 111111',
    'test test test V11 111 111 test test test' => 'V11 111 111',
    'test test test V1 111 111 test test test' => 'V1 111 111',
    'test test test E111 111 test test test' => 'E111 111',
    'test test test V11111111 test test test' => 'V11111111',
    'V1111111 test test test  test test test' => 'V1111111',
    'test test test V111111 test test test' => 'V111111',
    'V 1111111 test test test' => '1111111', // Missing Letter
    'test test test V 1111111 test test test' => '1111111', // Missing Letter
);

Answer 1

? only is a quantifier after groups or literal chars or characters classes e.g.

If ? occurs after another quantifier * or + and {n,m} it will just make the matching less greedy. Meaning the regex will try to match the least amount.

So \d{1,2}? does not mean optional. It means match one or two, but prefer to match just one. You meant to write \d{0,2} instead.