I go to sync my phone and it says,"The iphone could not be synced because this computer is no longer authorized for purchased items that are on this iphone". When I go to authorize it says it's already authorized. ios9.3.1, iphone 5s

Hello dinukago,

Thanks for using Apple Support Communities.

From your post I understand you're getting an error that your computer is not authorized for purchased items on your iPhone. Since you have tried to authorize already, and know your computer is authorized, then it appears you have content from another Apple ID on your iPhone. If you have any other Apple ID's then please authorize your computer in order for it to be synced.

Authorize your computer in iTunes

Take care.