Starting next week - Gamertags will not link to Windows Phone games.
This means you will not be able to earn any achievements for ANY windows phone game after this week, including Spartan Assault and Spartan Strike.
If you want those achievements (because they’re separate per platform) you have less than a week to do it.
May 16th they cut off.
https://www.windowscentral.com/microsoft-shut-down-xbox-services-windows-phone-may