My next phone...

What is the phone you currently own & specifically for Pokemon Go heck no, but a 4gb ram phone could be quite useful outside of this game.

Samsung s6.

for phone buy samsung s7 or s8 recomended. or One plus. just for now the app is a bit laggy due to updates, all are experiencing gym glitches right now and lag.

It works on my 1 GB phone and most of the time the reason for a restart is a network problem rather than PGs notorious memory leaks, so I don't think 4 GB would give a significant advantage over 2 GB.

Yes it will, and for a lot of other applications too, however remember sometimes is not about the phone is about the network and servers from the game, so dont expect zero lag

one plus 3
samsung s7
would be reccomended for high end android smartphones

With 2GB is enough for this game...
The problem is the server not the phone...

I hate bulky case to protect phones, and if you're like that, simply go Samsung S7. Price is dropping (S8 is around the corner), and the phone is waterproof which is great if you get caught in the rain or snow and still want to keep playing. Niantic has hired lots of new programmers, so a few of them will likely be able to clean up their code eventually, so it won't be such a ressource heavy hog eventually....

Otherwise, go with the phone with the biggest battery so you don't have to carry a car battery with you when you want to play more than 2-3 hours ;)

I use one plus 3T with 6gb of ram. Battery last an eternity. Rather cheap and great phone for me