I appreciate your help! I should have provided more detail. Here's the full picture (hopefully):
There are two of us sharing one iMac computer which has a profile for each user on it (including iTunes). We both have our own iPhones as well. To date, we've been sharing the same iTunes account and the same iCloud account name. So, you can imagine the mess of overlapping information on the two phones.
My goal is to leave my account as is. But to take my husband's iPhone and create both a new iCloud and separate iTunes account in his profile on the iMac. I'm thinking this will keep everything on his phone in sync with his iMac profile, and everything on my phone in sync with my iMac profile.
If that is accurate, that means that I do not need to make any changes on my phone or profile. But I will need to make the changes in his iTunes account, as well as to create a new iCloud account name and password for his profile and phone. How do I do that, if I'm correct?