Display TMS layer in an ArcGIS Online Map

For ArcGIS Online you need to include the subdomain variables (i.e.'a,b,c,d'). So under the Subdomains space you will need to enter a,b,c,d, or a,b,c if that does not work. You will also need to alter the TMS URL to http://{subdomain}localhost/Mapas/2014/bing_roads_en/{level}/{col}/{row}.png.

You do not need to add the subdomain, that parameter is optional and is only used for services that support it. For example, some tile providers have multiple subdomains to allow you to send requests to many servers to get faster responses. That's what it would be used for. I doubt your local server has that kind of setup, so don't worry about it.

Since you are hosting locally, your URL is currently http://localhost/Mapas/2014/bing_roads_en/{level}/{col}/{row}.png, and that looks right. One thing I'm wondering is if you set the extent when you added the layer?

In ArcGIS Online, go to Add - Add Layer from Web - and then select "A Tile Layer". Then put the URL you provided in the URL field. You have to populate the other 2 fields as you know. Then click "Set Tile Coverage" and accept the default (it should be the set to the whole world, essentially).

Please clear your browser cache or use a new incognito mode session while you are troubleshooting this, as otherwise, you might still see old, cached tiles.

I also noticed you are using the layer as a basemap - does it make any difference if you add it as a regular layer instead?