Not that this is a complete shock, but you can no longer purchase a Windows Phone online via the Microsoft Store. As noted by VentureBeat, Microsoft is no longer selling Windows phones because they are "out of stock" or they simply gave up trying to sell the phones with a dead OS.
Windows Phones might still be available for "pickup in store" as indicated in this tweet (with screenshot) by Rich Woods of Neowin.
— Rich Woods (@TheRichWoods) April 19, 2018
This was a long time coming with the death of Windows 10 Mobile, but there are still some Windows Phone fans looking to get Windows 10 on ARM working on some Lumia devices. If you are still in the market for a Windows Phone, you can stop in and see if there are any remaining stock at your local Microsoft Store.
Otherwise, you can hold out hope that Microsoft will release a Surface Phone or give up and get a Samsung Galaxy S9+ or Razer Phone. Both are available now in the Microsoft Store.