How do I get Safari back on my home screen its disappeared

Phil0124 is correct when referring to modern iPhones on recent versions of iOS (14 or later)… However if you are using an iPhone 5S on iOS 12, the App Library does not exist on your device.

There is also the possibility that Screen Time Content & Privacy Restrictions have been enabled, which under some circumstances can cause Safari to “disappear”. If that is the case, Safari simply needs to be re-enabled in Settings > Screen Time > Content & Privacy Restrictions > Allowed Apps

Safari is not one of the apps that can be deleted.

Check other Home Screens, or in folders.

Also, check the App Library. You can drag ti back to a Home Screen from there. click here ➜ Organize the Home Screen and App Library on your iPhone - Apple Support