Treat a lost phone as a security issue as well as a missing device. The phone may contain email, banking, messaging, photos, saved passwords, and authentication methods.
Use the official device-finding service for your phone to locate or lock it if available. If recovery is unlikely, follow the service's options for protecting or remotely erasing the device.
Contact your mobile provider if you need to suspend the SIM or replace it. This can help prevent someone else from receiving calls or messages intended for your number.
Secure important accounts, especially email, banking, and messaging. Review signed-in devices and remove the lost phone where the service allows it.
If you believe the phone was stolen rather than simply misplaced, continue with the phone-stolen incident guidance.