There are a lot of ways people can gain access to your phone. One of the easiest cloning methods you can prevent is leaving your phone (and its SIM card) unattended. SIM cards can be duplicated and used in another device. If you're visiting a crowded place it's a good idea to turn off the Bluetooth, WiFi, and NFC. While highly illegal, some attackers use scanners to hijack your IMEI. Turning these functions off while in public helps to prevent access. Lastly, you can use a third-party application to secure your phone and alert you to attacks.