Hello NiKo22,
Thanks for asking the Apple Support Communities for help with your iPhone not responding properly when you receive a call.
Please start by forcing the Phone app to quit: How to force an app to close on your iPhone, iPad, or iPod touch - Apple Support
Then, restart your iPhone: iPhone User Guide: Restart iPhone - Apple Support
If your entire device is still freezing, try this article: If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support
If you still have issues, it may be beneficial to reinstall iOS using your computer. Before reinstalling you should make a backup of your data before the next steps. You can make a backup in iCloud or iTunes using this article: How to back up your iPhone, iPad, and iPod touch - Apple Support
After your data is backed up, you can reinstall iOS using iTunes. The reason we need to use iTunes for this step is to get a new copy of iOS installed to your device. Use this article to reinstall the iOS: If you can‘t update or restore your iPhone, iPad, or iPod touch - Apple Support
Please pay close attention when you reach step 4. Once iOS is reinstalled, test if the issue or issues are still occurring.
Thanks again and have a great rest of your day.