Official Pokemon Go app is apparently never coming to Windows Phone Devices. However, the third-party Pokemon Go app is once again available for Windows 10 Mobile Devices. The game is dead on every platform but if you still want to play Pokemon Go on your Windows Phone Device, you should get the third-party app.
The developers of PoGo, the 3rd party Pokemon Go client stopped updating the app but a new version of the game has been released after a long gap. POGO-UWP now uses a slightly modified version of AeonLucid, which is more maintained. You can download the game on your Windows Phone and open it from file explorer after enabling developers mode.
We currently do not know as to how long will the game be working on Windows 10 Mobile. It is worth noting that the PoGo UWP app is not an official app and you might lose your Pokemon account. You can download the game by clicking on the below link.