Is it common for hotels in Philippines to have only ONE bed sheet?

Yes, that's common - particularly in cheap hotels or guest houses. The mattress cover is designed to be slept ON, sleep UNDER the sheet (and blanket if you're cold).

If it really bothers you, just ask for an extra sheet.

Have stayed in many hotels in many cities in the Philippines, from 5star to no star and have never seen that

Hard beds, paper thin sheet, noisy aircons, street noise with roosters and dogs, plus koroke!!!!! Inspect the room first because there is no refund once they get your money in their greedy fingers

You likely stayed at a cheapo hotel. Break out the visa and stay at a nicer place.

No, granted I am speaking from 1 9 day trip I took there, but typically do to the weather the hotels usually only put sheets on the bed and have blankets available on request, but otherwise its like anywhere else in the world, they put 2 sheets on, I am just guessing someone goofed setting up your room and there is probably sheets in the dresser

You need to stay in 5 star hotels to have better comfort of beds.

Philippines is still a developing country and the people are quite laid back and easy going, hence the lack of service standards in certain hostels or hotels.

That is NOT common here. I have been retired & living here for 8 years now plus the 7 two months long vacations before that & I have NEVER encountered that situation.

However what is common is when a foreigner makes a simple request for anything he is stared at (even more than usual) like he is crazy

a six pack and 1 prostitute for an additional $5 dollars