He can get a Visa from the Philippine Embassy in UK
or he can enter Philippines for 21 days without any visa and just pay for extensions at an immigration office when he's there.
Here's the general Visa Information page for a UK application.
Here is the form for Application For Non-Immigration Visa together with guidance notes and fees
Here's some good information on Visa Extension Fee's from the The Bureau of Immigration in Philippines website.
And more useful information can be found here too. (also from The Bureau of Immigration)
I hope you won't mind if I just make some comment on the overall plan you both appear to be following.
Have either of you considered the potential visa application impacts of him actually staying in the Philippines for 6 months?
I'm really thinking about how your fiance sees himself being able to meet the Financial Requirements given that solid evidence is needed to either prove a gross income of £18600 prior to application (with pay slips and bank statements etc) or
when he's returning with the applicant to the UK to work, he must have solid evidence of confirmed salaried employment in UK (starting within 3 months of return).
This employment must have an annual starting salary sufficient to meet the financial requirement applicable to the application.(currently £18600 for a couple)
Sorry to get of topic with that, just trying to help with the bigger picture.