Difference between IRS and phased array/reflectarray
Phased arrays have a number of transmitters/receivers in parallel that vary the phase in order to digitally form a lens.  This lets the transmitters/receivers adjust its gain in each direction digitally.  IRS are (usually) passive devices that vary how an incoming signal (possibly from a phased array, MIMO device, etc) reflects in/out of a space.  They're conceptually similar, and a reflective IRS with a directional antenna pointed directly at it would effectively be a phased array.
For more information, the introduction of this paper compares IRS to MIMO and related technologies:
https://arxiv.org/pdf/1907.04789.pdf