Greetings Sarahjoanne,
If your iPhone is unexpectedly restarting, these are the best steps to take:
"Check your software
Make sure that your device has the latest version of iOS or iPadOS and that your apps are up to date. If the issue continues after updating your software and apps, check your hardware.
Check your hardware
On an iPhone 6 or later, check your battery health under Settings > Battery > Battery Health.
If your battery doesn't need service, and your iPhone, iPad, or iPod touch continues to frequently restart or turn off, contact Apple Support.
If your apps quit unexpectedly, learn what to do.
If your device has a frozen screen, doesn't respond, or becomes stuck when you turn it on, learn what to do for iPhone, iPad, or iPod touch." If your iOS or iPadOS device restarts or displays the Apple logo or a spinning gear unexpectedly
We hope this helps!
Sincerely.