Why my iPhone keeps freezing and crashing?

Perform a backup, factory reset, and restore, if you can.

Restore your iPhone, iPad, or iPod to factory settings - Apple Support (includes links to backup, restore)

Failing that, contact Apple Support. Use the Support link in the lower left corner of this webpage, and chat or call Apple as available.

There can be multiple causes, let's start with a few basic checks.

1. Is your phone up to date at Settings > General > Software Update?
2. What does your battery info show at Settings > Battery > Battery Health? The % and does it say it's at peak performance?