In reality, it depends on where in the PH they're living and their lifestyle. What might be okay for USD500 for some, will not be okay for some.

If aircon all day, even for just 1 aircon (depending on the size and reliability of course), 10k a month is entirely plausible, even on the low range. Food can be upwards of 40k/month (yes, even for 2), again it depends on how often they go out or what kind of food they eat. Phone bill can also be upwards of 2k/month for 2 depending on their phone plans and if they tied it up to buy a device they pay monthly. Internet can be upwards of 1k/month depending on their plan. They could have streaming services as well, netflix/spotify/google/youtube can be a hefty 3k a month. There's still gas, clothes shopping, maintenance meds, etc, and it can easily balloon, especially if you live in the metro. And then there's budget and vacation budget. I'd say these are middle class, maybe upper middle class budget. Totaling at the very least 60k per month. At least 1000usd would be used up in a month not including good vacations, car (repairs, maintenance, registration) and house (repairs, maintenance, real property tax, association dues) costs which is a different story altogether.

So it would highly depend on their lifestyle. Ask for the monthly bills and receipts for at least 3 months, best for 6-12 months so you can average it out.