change apple id on current phone

Sign that AppleID out of iCloud, FaceTime, messaging, the App, music and book stores. Then sign back into all those with the new AppleID.

If you don’t want your personal AppleID data on the phone to merge to your new AppleID’s iCloud account, you will have to erase it first, then simply set it up as new using that new AppleID.

Go to Settings, then your Apple ID (right at the top), then Sign Out (all the way at the bottom).

If you want to make sure there are no remnants of your personal data remaining, go to Settings -> General -> Reset -> Erase All Content and Settings. Then set it up as a new device with your work account.