Our child is a UK and Ph passport holder

Hi everyone! So just recently, I posted a question here in regards to our child's first child UK passport. It was approved few weeks ago. We applied from Manila. I was actually surprised it got approved only days after submitting all the necessary documents.

So now, our child is a UK and Ph passport holder and that makes him a dual citizen right?

Our question is, is he really considered an automatic dual citizen or does he need to secure a document after acquiring his UK passport? I'm just thinking once we try to travel abroad and comes back in the Ph, BI might look for some documents.

Does anyone here have the same status? Hope you can help us!