My son can't speak clearly or should I say he can't speak any clear word except mama.. he's fathe ris korean and I'm a filipino... He can understand what I'm saying sometimes.. he can write aan alphabet complete and always want to watch a video likes phonics.. please help me I don't know what to do

It is very difficult to know without a lot of testing, because a child who doesn't talk much might have absolutely nothing wrong at all and grow up to be a doctor or Einstein.
The things that might be wrong, IF there is anything wrong:
1. He can't hear normally. Have someone softly walk to a doorway behind him and speak his name in a normal tone of voice to see if he turns his head.
2. He's autistic.
He doesn't sound autistic. So if his hearing is OK, then I would hope that there is nothing wrong with him at all! Many famous and successful people didn't talk for several years.
He may need to socialize with other children more?

I have two students in my class this year who never speak unless spoken to. Their parents speak different languages, neither being English. So, they definitely have issues with some language confusion. These children do speak, but very little at all.
What languages do you speak at home? Are you and your husband speaking English or are you speaking your home languages?
Definitely seek the help of your pediatrician to rule out some of the medical issues. Make sure your child vocalizes the need for something (water, food) instead of allowing him to point or just giving it to him.
Keep telling him the name of anything you see or cook with or do. Make him repeat it back.
Let us know what you find out!