Please make sure that you have Windows OS 8.1 or above in your system.
Install Visual Studio Community 2015. Please do select 'Cross Platform Mobile Development' on 'Select features' page while installing visual studio.
Now you should be able to perform below command for Windows Phone platform in your ionic project.
$ionic platform add wp8
$ionic build wp8
After successful building, open Visual Studio solution from platforms/wp8 folder and run the project.
I would suggest you to choose Windows Phone 8.1 emulators.
Note: First launch of Windows Phone emulators take good amount of time. 