Final answer:
To best ensure the privacy of data on a phone left in a taxi, a Remote Wipe is the most effective option as it erases all data and restores factory settings, preventing access to private information.
Step-by-step explanation:
If a user realizes they left their mobile phone in a taxi, the best course of action to ensure that none of the private data is accessed is D. Remote Wipe. A remote wipe can be initiated through specific services or device managers available for smartphones. This action will erase all data on the phone and restore it to factory settings, ensuring that no private information can be accessed even if the phone falls into the wrong hands. While a passcode lock is a good first line of defense, it can potentially be bypassed. GPS tracking is helpful for locating the device but does not protect the data if the phone is accessed before it is recovered. A remote backup is useful to save your data, but it does not protect the data on the actual lost device.
It is also worth noting that with the right software, law enforcement and criminals have the capability to remotely activate a phone's microphone and camera. However, a remote wipe would disable the phone entirely, preventing such intrusion.