outlook 365 endless synchronizing

Hi 

I am using outlook in office 365, the latest version. when i open outlook, it completes send/ receive and then starts to sync incoming inbox. It is endless and slows my outlook and computer down, i can't even use my emails on my phone. 

when outlook is closed on the computer, my emails work normally on my phone. 

If anyone can help me fix this that would be much appreciated 🙂

James