Do my themes back up across devices in Microsoft SwiftKey Keyboard?

Your purchased themes and content are all backed up to your Microsoft SwiftKey Account. 

When you download Microsoft SwiftKey Keyboard on your new phone or your other Android devices, be sure to sign into the same Microsoft SwiftKey Account that you used to purchase your content from the SwiftKey Theme Store. Your purchased themes should show as available to download.
 

Note:

• Themes cannot be synced across Android/iOS platforms.
• It is not currently possible to use Backup & Sync to save your Photo themes to your Microsoft SwiftKey Account.

Can I transfer themes from Android to iPhone?

All themes are unique across platforms, and cannot be transferred from Microsoft SwiftKey Keyboard for Android to iOS (or vice versa) at this time.