How do I sync the notebooks on my computer with my iPhone?
Any notebook that you want to access from your iPhone must be located on OneDrive or SharePoint. Notebooks created in versions earlier than OneNote 2010 will not sync with your iPhone.
On your Windows computer, do the following:
Start OneNote and open the notebook that you want to access from OneNote for iPhone.
Select File > Share and choose a OneDrive or SharePoint location for the notebook.
Follow the instructions on the screen.