How to write a file.txt with PHP from HTML, with the code on a server

What happens is that I am writing according to the information of a telnet connection with php, but I only manage to create the file when I open the file from the server console in SecureCRT with the command "php file.php", but from the web I do not edit the file or create it or anything, ideas?

function conexion($central,$ip){
    if (file_exists("/var/www/html/saraweb/datos_centrales/datos_".$central.".log")){
        unlink("/var/www/html/saraweb/datos_centrales/datos_".$central.".log");
    }
    echo $central;
    echo $ip;
    $central1 = $central;
    $da = fsockopen($ip, 5001, $errno, $errstr, 10);

    if (!$da){
        echo "$errstr ($errno)<br/>\n";
    } else {
        $entrada = "user\r\n";
        $entrada .="password\r\n";
        //$entrada .="allip;\r\n";
        $entrada .="alstp;\r\n";
        $entrada .="exit\r\n";
        fwrite($da, $entrada);
        while (!feof($da)) {
        $salida = fgets($da, 128);
            echo $salida;
            eventos($central1,$salida."\n");
            echo "<br>";
        }
        fclose($da);
    }    
}

but then I do not know how I know how to make it run from the web in HTML as it does from the connection to the server in SecureCRT