how can i get my koseki tohon

My father is a Japanesehe is married with my mother. I am currently staying in pilippines right now. All I want is to get my Koseki Tohon so that I can try to find my way to Japan easily and find a work there. I think my father did not register a Koseki Tohon for me. How can I get one?

Your parents had to register your birth within 14 days of birth(if in Japan) or within 3months (if overseas).
I'm not an expert, but if he didn't register then, you are not a Japanese national right? As in you don't really exist on Japanese record?
You could ask Japanese embassy in Phillipine for the best answer and advice.
Normally, when you are registered and need to get Koseki Tohon, we walk in to Japanese embassy.

where were you born, Japan or Philippine ?

Where he/she was born doesn't matter, his father is Japnese, so he has right to claim for Japanese nationality.

Yes, it doesn't matter where you are born.
but it does matter how old you are now.
If you are over 20 years old now and you think father didn't register your birth, well....it's gonna be very difficult I guess...

The firm evidences that the father has Japanese nationality are necessary. You might find out some information from the public authority where you were born.
If you were born in Japan, your mother reported your birth to Philippine Embassy in Japan to have your passport. There should be some record. (generally, father's name, birth date, address, etc. should be there.)
If you were born in Philippine, you may get similar information in your country.

I think, it is not obligation that a Japanese reports a new born baby, if he/she is married with a foreigner and has a baby outside of Japan.

Where he/she was born doesn't matter, his father is Japnese, so he has right to claim for Japanese nationality.

The right only extends up to a point, as there is a time limit to claim citizenship (23 yrs old I believe, but check with an official source). After that you have to go through the regular naturalization process.