on paper, 32 GB is the max for many, but I've heard of a 520 and 1520 taking 128 GB cards despite spec sheets so... (I've only really seen 64 GB as the limit by it still works though...)
The phone will handle a 128 GB micro SD card. The reason that "on paper" you find 32 GB is because when the phone was introduced the 32GB was the max card which was available in that time. And for newer phones the "on paper" spec is 128 GB because that is now the largest micro SD card available.
Or in other words it is not the phone (or tablet, or other windows device) which determines the max size of the SD card but the "(economical) manufacturability" of a such a SD card.