Amazon’s customer service phone number in the US is 1-888-280-4331, and you can call that number at all times of the day. Once you've placed the call, you'll be greeted by an automated system.

It’s important to note that customers should have a cell phone number connected to their Amazon account. Customers must enter verification codes that will be messaged to their linked contact ...

and Reddit threads to actually talk to a human over the phone. As you probably already know from trying to contact someone on Amazon's "Contact Us" page, there is no direct number to call.