Why are the text messages of two Apple phones synchronized?

This is because two iPhone use the same Apple ID, and the SMS function is turned on at the same time.

Use a different Apple ID or turn off SMS to enjoy this feature. Take the iPhone 7 as an example. The specific method is as follows:

Step 1: Click "Settings" on the phone desktop.

Step 2, drop down the menu in the setting interface of the mobile phone, and then select the "Information" option.

Step 3, turn off the switch in the "iMessage" column.