I have two phones that share text and I need to separate them

Each iPhone would need to be using a separate Apple ID. Unless you own and use both iPhones, you should not be sharing an Apple ID with anyone.

Sign out of the Apple ID on one of the iPhones, and sign in with another Apple ID, then delete any content belonging to the Apple ID you signed out from.

Settings ➜ Account (top go Settings) ➜ (Scroll Down) Sign Out

Settings ➜ Account ➜ Media & Purchases ➜ Sign Out

Settings ➜ Messages ➜ Send & Receive ➜ Apple ID ➜ Sign Out

Settings ➜ FaceTime ➜ Apple ID (below Caller ID) ➜ Sign Out.

You will need to delete all Apps and content downloaded with the first Apple ID as they remain tied to it, and in the case Apps will forever require it to update.

The best option, is to simply erase one of the iPhones and set it up again with a different Apple ID.

How strict do you want these controls?

If this is a case of having, say, a personal and a work phone, and you don't want to get work messages on your personal phone, and vise versa, then it may be as simple as disabling iCloud synching via Settings -> AppleID -> iCloud -> Apps using iCloud and turning off Messages.

Your phone will still receive SMS text messages, but iMessages now won't be seen.

You can adjust the settings on each phone as needed.

This may be enough to give you an air-gap between the phones, but it can easily be undone (by re-enabling Messages in preferences), so it may not be a solution if the phone is in use by someone else and you don't want them to see the other messages.

Do you own/use both iPhones? Or does someone else use one and you are still logged into that one?