Like other airlines, they give you the option to place a bid on paid upgrades where they show a scale of your chances for the upgrade ranging from poor to strong.

For MNL-SFO poor is at $700 one way and strong is $1400 one way, while bkk-mnl is $140-300 one way.

Any experiences on getting upgrades on the lower end of the upgrade price?

https://www.philippineairlines.com/mypalupgrade