Decide on your localisation and culturalisation strategy.
Before going further, I should make it clear that this advice is from the perspective of somebody who localises existing source material (not a writer). That is, you should apply this on top of the other good advice from source writers here.
When creating any new content, even if it will eventually reach a foreign market, it is always best to stick to the language and tools that allow you to write to the highest-quality.
As this story is focused on Filipino POV; it's likely your native language will give you the most freedom to describe and showcase the character journey. That is, you want to write this in your native language - and follow up with localisation and culturalisation.
So, what is the difference between localisation and culturalisation?
At the top level, the thing to keep in mind is that localisation is simply turning your text from your source locale into a target locale. That is generally accomplished by simply translating the text - trying to find as close an equivilent as possible in each language.
Worth noting, is that the goal is to simply make the source text comprehensible in another language. That is, even though the text is now written in English - the mannerisms and speech patterns will still be reflective of your Filipino source material.
In some cases, this may be desired - making it clear that the text comes from a foreign source. But in general, most good translators will apply some form of culturalisation to help convey a similar emotional journey in another language.
Culturalisation is the step further - actually changing certain actions and sections of your source text, to make it culturally acceptable in another market.
This could be something simple such as changing a greeting between two friends from strictly formal (Japan), to something much more casual (US). As culturally, these are the normal ways to greet in each (where keeping the formal greeting in US English would convey something different about your characters than you meant to).
But it could be something more, such as changing a main character's hobby from gambling on horses (fairly acceptable in UK) to something pretty different, in markets where gambling would specifically mark your character as having "low morality".
Of course, most good translators will apply a certain amount of this naturally, and again, most good translators will communicate with you regularly to ensure they are making the alterations you want - and not going too far/too little. But it's a factor you need to consider in how you want the story to be percieved in a foreign market.
Putting this together
What this means for how you write, is that while you are able to personally write in English - you need to be conscious that you will not necessarily be writing culturally in English.
Importantly, even when writing in English - there is no single English market. The culture in the UK, US and in countries where English is a second language - are all vastly different (even if all of them can "read" the story without issues).
To be clear though, this is not an assertion that you need to have everything culturalised and localised professionally. But only by being conscious of these issues, and how your writing will be percieved, can you be confident that your story will be percieved how you want it to be.
Again, writing in English yourself is a perfectly valid choice (and any foreign vibe it gives off may be desired for your story) - but it should be seen as a conscious decision in terms of your culturalisation strategy and not a default.