It is safest to avoid using public USB charging ports and take other steps to protect your phone. Here are some ways to do this:

1. Do not plug your phone into unfamiliar USB ports – without knowing its source, you won't be able to know if it is secure.
2. Only use your own charging cable – USB cords are all made differently, and by using your own, you can guarantee that it won't lead to any malicious activity.
3. Make sure your phone is password protected – in case of theft, it will make it difficult for the thief to access your data.
4. Be mindful of your phone’s power settings – if you allow it to run out of juice completely, your phone might not be able to charge until it is restarted.
5. Use a tracking app – consider tracking your phone so that you can locate it if it goes missing.