CODE EXAMPLE FOR PHP

check if phone number is valid php

   function isDigits(string $s, int $minDigits = 9, int $maxDigits = 14): bool {
        return preg_match('/^[0-9]{'.$minDigits.','.$maxDigits.'}z/', $s);
    }

    function isValidTelephoneNumber(string $telephone, int $minDigits = 9, int $maxDigits = 14): bool {
        if (preg_match('/^[+][0-9]/', $telephone)) { //is the first character + followed by a digit
            $count = 1;
            $telephone = str_replace(['+'], '', $telephone, $count); //remove +
        }

        //remove white space, dots, hyphens and brackets
        $telephone = str_replace([' ', '.', '-', '(', ')'], '', $telephone);

        //are we left with digits only?
        return $this->isDigits($telephone, $minDigits, $maxDigits);
    }

    function normalizeTelephoneNumber(string $telephone): string {
        //remove white space, dots, hyphens and brackets
        $telephone = str_replace([' ', '.', '-', '(', ')'], '', $telephone);
        return $telephone;
    }

// how to use 
$tel = '+9112 345 6789';
if (isValidTelephoneNumber($tel)) {
    //normalize telephone number if needed
echo normalizeTelephoneNumber($tel); //+91123456789
}