Safest way to ship iPhone from US to Japan

Has anyone shipped a cell phone from the US to Japan?
What's the safest way to do so?
I want to use my relative's unlocked iPhone.

One time, I sent a cell phone from California to Japan via DHL. I chose DHL because their office is near where I work, and they are a little more economical than FedEx. If you donft need the next day service, you can use USPS or others.

Once I sent an iPhone from Japan to the US (the opposite direction) via Japan Postfs EMS, Express Mail Service, which may be equivalent to US Postal Servicefs Global Priority service in terms of tracking capability and speed.

The postal service tends to be picky about lithium ion battery in parcels (I needed to state that it was a gbuilt-inh battery) so you might be faced with the same question when you ship it if you use post office.