Yes, Hong Kong Postal do deal with post to Nigeria... But as you are posting something rather expensive, I would suggest to post it by Recorded mail at Hong Kong Postal...
At the same time, you will require to fill in a immgration form about what is inside the box... I would suggest you to not say it is anything expensive... Just devalue your phone to say 'gift' and devalue the price to three digit number instead of four...
As I can tell you even in a Advance country like UK, there are postman would would steal post... But generally Recorded mail is much safer as you will have a code given to yo which allow you to tract the location of the product...