How do I stop my iPhone and iPad from syncing? They currently sync website history, texts, and calls. My iPhone is company owned and iPad is personal.
Apparently, you have signed into iCloud on both your devices using the same Apple ID. Devices setup with the same Apple ID sync a lot of user data between them for built-in apps by default.
If you concerned about keeping company and personal data segregated, it is recommended to use different Apple ID for your iPad and iPhone (personal Apple ID for iPad and a separate one for iPhone).
Alternatively, if you have reasons to use the same Apple ID, you can selectively choose which data to sync. On your iPad/iPhone, go to Settings app → Tap on your name and picture shown on the top (Apple ID, iCloud, iTunes & App Store) → iCloud and under Apps Using iCloud section, turn-off the switch in front of all the apps for which you do not wish to sync data.
Specifically, to disable syncing website history, turn-off iCloud for Safari (it will also stop syncing bookmarks and open tabs from one device to the other), for text messages, turn off iCloud for Messages. If the SMS from your iPhone are also showing up on your iPad, you will additionally need to disable Text Message Forwarding on your iPhone. For that, go to Settings app → Messages → Text Message Forwarding and turn off the switch shown in front of your iPad.