Set a strong, unique password or PIN for your phone and enable biometric authentication methods such as fingerprint or facial recognition.
Enable data encryption on your phone, which scrambles your data and makes it unreadable without the correct key.
Keep your operating system and all apps up to date by installing updates as soon as they become available.
Avoid using public Wi-Fi networks for sensitive transactions and use a Virtual Private Network (VPN) when accessing the internet from public places.
Regularly back up your phone's data to a secure cloud service or an external storage device.