Monthly charge for AppleCare+

On an iPhone go to Settings->Account (top of Settings)->Subscriptions->Apple Care+

If you don't see it there, then you aren't paying monthly on that specific device.

You should also be able to see your Apple Care+ status in Settings->General->About->Coverage

No, not on the Apple website, the monthly charge is tied to your Apple ID used on the device that it was applied for.

As mentioned, you should be able to view the subscription in Settings on the device in question assuming its logged into the Apple ID that holds the subscription.