If I purchase iphone 16 from Apple USA Website while I’m in the Philippines, is it going to be locked or is it an open line?

You can purchase an unlocked iPhone from the US Apple Store. But I doubt they'll ship outside of the country, though of course you can ask.

The US iPhone 16 will not have a physical SIM slot. It'll be eSIM only.

Regards.

Apple online will not ship internationally.

Also your payment method will have to match the country of sale.

US iPhones are eSIM only.