What are your exact concerns as far as what could happen?
Are you asking if you transferred contents of your non-apple device over and what if there was malware you brought over in the process unknowingly? iPhones are more secure in that regard because you, the user, aren’t able to give access to the most privilege heavy parts of your phone’s system. In other words, processes can’t peek at other processes and this makes it difficult (but not impossible) for malware to get into things like the encrypted system files, etc.
As far as someone finding a phone and cloning it-phone contents, like with backups, are encrypted and aren’t going to be used in a different device without your permission or credentials. You would have to provide the security information to get into that.
As long as you use safe security practices like not reusing passwords, having two factor authentication, and secure your device with a code, enable Face ID, and pay attention security alerts, you’ll be fine.