Books not purchased in ibooks syncing from ipad to iphone?

My boyfriend has an entire library full of books on his computer and he put some of the ones I wanted in my ibooks on my ipad, but they will not sync with my iphone? Does anyone know a way to get them to work like books that i personally purchased or downloaded on one of my devices? They work perfectly normal on my ipad, but I want to be able to read on either device.

Any suggestions?

Thanks!