I have purchased personal content on these devices during the time i have had them.
Did you use your personal AppleID or your work AppleID?
Purchases are permanently tied to the AppleID you purchased with.
You cannot transfer them to another APpleID.
I would like to keep the content i purchased on the work devices but when I have tried to sync, they ask me to erase the phone first before syncing.
I don't understand.
Are you trying to sync your personal iPhone to a new computer?