Hello marydale23,
Welcome to Apple Support Communities!
We want to help resolve the issue so you're able to reply to your messages without the screen freezing.
Try a normal restart first to see if that helps:
"How to restart your iPhone X, 11, 12, 13, or later
- Press and hold either volume button and the side button until the power-off slider appears.
- Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
- To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo."
Or see here if you have a different model: Restart your iPhone - Apple Support
Please also check for any pending iOS updates, which can help make sure the software is working as expected. This Apple Support page can help get those updates installed: Update your iPhone, iPad, or iPod touch - Apple Support
"Update your iPhone or iPad wirelessly
- Back up your device using iCloud or your computer.
- Plug your device into power and connect to the internet with Wi-Fi.
- Go to Settings > General, then tap Software Update.
- If you see more than one software update option available, choose the one that you want to install.
- Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do."
These steps can help resolve a software issue causing the screen to freeze.
Please let us know if you have further questions.
Cheers!