Hello JJ_910,
Welcome to Apple Support Communities. I understand from your post that the alarm clock freezes when you hit the snooze.
First, let's make sure that your iPhone software is up to date. The latest version is 12.1.1. If you're not on the latest let's go ahead and do that now.
Update your iPhone, iPad, or iPod touch - Apple Support
Before you update, we suggest making sure you have a current backup. It's always good to keep a current backup to keep your data safe. Here's a link to help complete a backup on your iPhone: How to back up your iPhone, iPad, and iPod touch
In order to isolate and fix this issue, you will need to restore your iPhone. Steps on how to restore an iPhone can be found here: Restore your iPhone, iPad, or iPod to factory settings
After the restore, you will need to set up your iPhone as “new” for testing purposes. If your issue continues after a restore, I would recommend reaching out to Apple Support directly. You can do so here: Official Apple Support
Let me know how it goes.
Cheers!