为什么这个PHP语句出乎意料地剥离了7？

I would love a fresh pair of eyes looking at my problem which is driving me mad. Any help would be appreciated.

From just 2 lines of PHP code im trying to strip the first '44' if a user enters it at the start of there phone number:

    $telephone = '44789562356';
    $telephone = str_replace(' ','',$telephone);
    $telephone = str_replace('+44','0',$telephone);
if(strpos($telephone,"44")==0){
        $telephone = substr($telephone,2);
        $telephone = '0'.$telephone;
    }

Why is it that it strips '7's from all the phone numbers?

Like Colin commented, you need to use a strict comparison === on the return from strpos() since it returns false if the substring is not found, and 0 if it's at the beginning of the string and false == 0 is true, and false === 0 is false.

Alternatively, you can use regular expressions to specify matching only at the beginning of the string like so:

if( preg_match('/^44/', $telephone) ) { ... }

Or do the replacment with it:

preg_replace('/^44/', '0', $telephone);

Your code can be simplified to the following:

$telephone = '+44-789 56-2356 ask for larry';
$telephone = preg_replace('/[^0-9]/','',$telephone); // remove all non-numeric characters
$telephone = preg_replace('/^44/','0',$telephone);
echo $telephone;
// output: 0789562356