Why am I getting an error when calling a webservice function?

I am coding a C# web api 2 webservice and would like some help to get a single item from a request to a webservice.

Here is the web service controller class code:

[RoutePrefix("api")]
public class ItemsWebApiController : ApiController

Here is the web service function:

// GET: api/Getitem/1
[Route("Getitem")]
[System.Web.Http.HttpGet]
[ResponseType(typeof(Item))]
public async Task<IHttpActionResult> GetItem(int id)
{
    Item item = await db.items.FindAsync(id);
    if (item == null)
    {
        return NotFound();
    }

    return Ok(item);
}

Here is the uri to the IIS website:

http://localhost/thephase

Here is the uri that I am accessing:

http://localhost/thephase/api/Getitem/1

Here is the error that is being displayed in the browser:

{"Message":"No HTTP resource was found that matches the request URI 'http://localhost/thephase/api/GetItem/1'.","MessageDetail":"No type was found that matches the controller named 'GetItem'."}

Here is the WebApiConfig code:

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        config.MapHttpAttributeRoutes();

        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );
        var appXmlType = config.Formatters.XmlFormatter.SupportedMediaTypes.FirstOrDefault(t => t.MediaType == "application/xml");
        config.Formatters.XmlFormatter.SupportedMediaTypes.Remove(appXmlType);
    }
}

The error states that the controller is named 'GetItem', and this is incorrect. Hence I am thinking that the problem is in the WebApiConfig route code.

If I remove the int id from the function, then the function is called correctly.

Here is the same function with no parameter:

// GET: api/Getitemnoparameter
[Route("Getitemnoparameter")]
[System.Web.Http.HttpGet]
[ResponseType(typeof(Item))]
public async Task<IHttpActionResult> GetItem()
{
    Item item = await db.items.FindAsync(1);
    if (item == null)
    {
        return NotFound();
    }

    return Ok(item);
}

The following uri accesses the function correctly:

http://localhost/thephase/api/Getitemnoparameter

So the problem has something to do with the int parameter.

Can someone please help me to get access the GetItem function with a parameter?