Personally I'd consider either LBC small box (takes weeks to deliver) or even a DHL small packet. I doubt DHL will take a cell phone with battery but worth checking with them.

I've had some mail delivered into Philippines and some not.
The oddest thing though is that any card or letter I sent that contained a banknote never ever made it. Sometimes the card did .....alone.

Don't know how they do it unless they steam open on a large scale