SDXC is an evolution of the SD / SDHC memory card standard. Whereas SDHC cards have a maximum storage capacity of 32 GB, the SDXC standard supports cards up to 2 TB (2048 GB) with speed up to 300MB/s.
Just as with previous versions of the standard, there is a smaller "micro" version designed for small devices such as cell phones. microSDXC cards have all of the same features of full-size SDXC cards; they are just smaller.
Any SD or microSD card larger than 32 GB is actually an SDXC or microSDXC card.
microSDXC cards are the same size and shape as microSD and microSDHC cards, and the standards are designed to be backward-compatible. In other words, a phone with a microSDXC slot will also accept microSD and microSDHC cards. But a microSDXC card will only work in a phone that specifically supports microSDXC.