[Logic_]

Calisthenics already gave you an answer - however, tell us the name of your "users" table and the column name that you use for phone numbers.

EDIT: Untested code - here's an example of how it could be done:

PHP код:

mysql_format(g_SQL, query, sizeof query, "UPDATE IGNORE "#TABLE_USERS" SET `PhoneNumber` = %i WHERE `UserID` = %i", phone_number, user_id);
mysql_pquery(g_SQL, query, "OnPhoneNumberUpdate", "ii", playerid, phone_number);
forward OnPhoneNumberUpdate(playerid, phone_number);
public OnPhoneNumberUpdate(playerid, phone_number) {
    if (cache_affected_rows() != -1) { // Since -1 refers to an error
        // Tell player there phone number was updated
        pInfo[playerid][PhoneNumber] = phone_number;
        return 1;
    }
    
    // Tell player the phone number is already in use
    return 1;
}