Working for a company probably 10 to 20% of what an enterprise developer working for companies like Fedex, UPS, CH Robinson, Landstar, Swift, CR England makes.
Independent depends on how many projects you accomplish per year. Also depends on if you have set up maintenance agreements on projects, etc.
There isn't a set answer. It depends greatly on the specific location, not just the country.
Coders in major cities that have a large tech hub tend to make a lot more than in sparsely populated towns that are far away from major cities. It's not a steadfast rule, but is generally true. The specific country makes a big difference too. I'm sure coders in Germany generally make more than their Polish counterparts, even though they're neighboring countries.
php coders get paid way less than other languages.. (and thats a GENERAL rule i have seen, stack overflow do an annual survey etc and they have proven this to be the case) but where i am i have seen laravel positions with at least 60k... and thats a good amount to live on
if you are after more money i suggest python, java or .net - most financial org use java and that can earn u big bucks..
The payscale website has quite a lot of figures for different countries & levels of experience that you can click through. The data seems to get pulled from job adverts so might even be vaguely accurate ;-)