simple_xml_manipulation.php

<?php

$xml = <<<XML
<?xml version="1.0" encoding="ISO-8859-1"?>
<Person>
  <Name>{name}</Name>
  <Age>{age}</Age>
  <Gender>{gender}</Gender>
</Person>
XML;

$data = collect(['name' => 'Paulo', 'age' => 29, 'gender' => 'M']) // $request->all()
    ->mapWithKeys(function ($value, $key) {
        return ["{{$key}}" => $value];
    });

var_dump(str_replace($data->keys()->toArray(), $data->values()->toArray(), $xml));

/*
string '<?xml version="1.0" encoding="ISO-8859-1"?>
<Person>
  <Name>Paulo</Name>
  <Age>29</Age>
  <Gender>M</Gender>
</Person>' (length=120)
*/