The real test is “how much of your labor is require to purchace an equivalent amount of ‘stuff’ in each economy.”
There’s an aspect of exchange rates that says, if I have $100 in the US, am I better by spending it here, or by converting it into something else like GBP and buying the same stuff over there. To some extent, it depends on what stuff you are talking about, but if you create a diversified “basket” of stuff that you would need to live, that’s the standard of comparison.
You can go a long way to understanding this relationship just by understanding that first part. That’s called Purchasing Power Parity, and it’s demonstrated by The Economist’s “Big Mac Index,” which compares the price of a Big Mac in various countries.
The other aspect of the economy is how much labor does it take to earn $100 worth of stuff. Food is cheap in many emerging markets, but it also takes the average laborer far longer to earn enough to buy it (which is one reason why it’s cheap, demand is lower at higher prices).
From a purely economic perspective, where you would rather live would be a function of both how easy/difficult it is to earn the money to buy the stuff you need. It might be more expensive here in the states than it is in the Philippines, but if you are earning a higher wage here, it can still take you less time to earn a nice meal here than it would over there. Ideally it would be best to earn here and eat there, but that’s not always a realistic decision.
Wages tend to be determined by productivity, but also by the supply and demand of skilled labor. Which is to say that the ability of firms to pay wages is determined by productivity, but the ability of labor to demand wage ingcreases in line with productivity gains depends on their bargaining power, which depends on things like the supply of labor with the relevant skills, regulations, and whether labor can organize collectively or not. Things like labor unions can constrain the adaptiveness of businesses, but it is also true that when labor is completely unable to organize and make collective bargaining arrangements, ordinary laborers get placed in inhumane conditions, and profits flow increasingly to the owners of capital.
Another thing to consider is the expected inflation rate. If the US has low inflation, while the UK has high inflation, it may be that 1 GPB is $1.60 today, but next year it’s going to be worth $1.40. If that’s true, then the pound is going to be purchasing less and less over time, and that’s really what’s important from an investment point of view. Even though a $1MM GBP account is worth $1.6MM USD right now, you don’t want to hold it if the real purchasing power (the amount of “stuff” you can buy) is shrinking faster than the USD’s.