Regex validate and correct telephone number

Question

At the moment I am validating and correcting given Telephone numbers with this version of code:

function validateTelephoneNumber($parameters){
    
    $validTel = "<^((\\+|00)[1-9]\\d{0,3}|0 ?[1-9]|\\(00? ?[1-9][\\d ]*\\))[\\d\\-/ ]*$>";

    $telNumber = $parameters;

    if (preg_match($validTel, $telNumber)) {
        $telNumber = preg_replace("<^\\+>", "00", $telNumber);
        $telNumber = preg_replace("<\\D+>", "", $telNumber);
    }
    return $telNumber;
}

what I want to get is:

|               input               |           return value            |     comment (only info)     |
|-----------------------------------|-----------------------------------|-----------------------------|
| 0043/2342/213412-1234             | +4323422134121234                 |                             |
| +43 234 2312341234 12             | +43234231234123412                |                             |
| 07234/32434                       | +43723432434                      |if no country prefix -> +43  |
| (0677)32423434                    | +4367732423434                    |if no country prefix -> +43  |
| 0049 171 12341234                 | +4917112341234                    |                             |
| 0031 9872 12341234                | +31987212341234                   |                             |
| 0043(07234)1234-1234              | +43723412341234                   |remove 0 in local prefix     |

Can you help? Thanks

Answer 1

The conversion of the telephone number (after validation) can be done in three steps.

Step 1: replace leading zeros with "43" if the there is no country code.

I assume there is no country code if the string contains exactly one forward slash or begins with a left parenthesis. To add the defautlt country code we can replaces matches of the following regular expression with "43".

^(?:\(0*|0*(?=\d+\/\d+$))

Demo 1. PHP's regex engine performs the following operations:

^              : assert beginning of string
(?:            : begin non-capture group
  \(0*         : match '(' followed by 0+ zeroes
  |            : or
  0*           : match 0+ zeros
  (?=          : begin positive lookahead
    \d+\/\d+   : match 1+ digits, '/', 0+ digits
    $          : assert end of string  
  )            : end positive lookahead
)              : end non-capture group

This will convert the strings

0043/2342/213412-1234
+43234 2312341234 12
07234/32434
(0677)32423434
0049 171 12341234
0031 9872 12341234
0043(07234)1234-1234

to

0043/2342/213412-1234
+43234 2312341234 12
437234/32434
43677)32423434
0049 171 12341234
0031 9872 12341234
0043(07234)1234-1234

Step 2: remove unwanted characters

For this step we replace matches of the following regular expression with empty strings.

^0+|[ +\/()-]

Demo 2. PHP's regex engine performs the following operations:

^          : assert beginning of string
0+         : match 1+ zeroes
|          : or
[ +\/()-]  : match one character in the character class

This will convert the strings obtained in Step 1 to the following.

4323422134121234
43234231234123412
43723432434
4367732423434
4917112341234
31987212341234
430723412341234

Step 3: Add '+' to the beginning of the string

This is most easily done with a PHP statement, producing the following strings.

+4323422134121234
+43234231234123412
+43723432434
+4367732423434
+4917112341234
+31987212341234
+430723412341234