My spouse and I have oth hers and my phone on the same Apple ID. This causes issues with emails and phone calls to each other. How do I change my Apple ID but not changing her Apple ID at the same time?

Indeed an Apple ID should never be shared, as you now realize.

Here are the steps you should follow:

1. Obtain a new Apple ID for one of you. Let’s say you get it for your spouse. Here’s how: How to create a new Apple ID - Apple Support
2. Thoroughly cleanse your spouse’s iPhone and any other Apple devices (s)he may own that are signed in with the wrong Apple ID. What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support
3. Your spouse then “moves in” to her/his like-new (software-wise) iPhone using only items enrolled under her/his Apple ID.
4. Family Sharing may then be instituted if you wish. Set up Family Sharing - Apple Support