I understand. I can obviously only give general pointers, and will do so here:
Parties that are entering into a contract may choose the country whose law applies to that contract. But other mandatory laws may also apply and regardless of what country’s laws an employer chooses for their employment contracts.
If the employment contract terms are contradictory to the employee’s host country, then local laws can prevail in setting the standard.
In your case, you need to check with a Phillipino lawyer to make sure that standard terms in the Philippines are not so contradictory to the UK as to render a UK contract term void.
Ultimately it's probably easier for you to operate under the UK law as you will have both a better access to resources and an understanding of the law if a dispute should arise.
I would suggest you consult with a Phillipino lawyer, as if there is nothing untoward in their mandatory employment laws you can simply elect the UK as the jurisdiction for the agreement.
I hope that this helps.
Thank you for your enquiry today. I am happy to answer follow-up questions - please do get in touch with requests for extra information or further queries and I will do my best to help you