With regards to the Philippines, it is pretty much uninteresting to apply the US-PH treaty: Withholding tax will still be 25%, compared to the standard 30%-rate.
As you said, most brokers will anyway deduct full WHT, specifically the ones in SG.
If one follows a dividend strategy, better opt for countries with zero or very low WHT. There are plenty of them with a wide selction of stable dividend payers. US stocks are best avoided in that context.
Another idea would be to look for an ETF/ mutual fund with Irish or LUX domicile︀ which invests in US-dividend stocks.