I have more information, I have narrowed the problem to the width of the channel:
option htmode 'HT40'
# option htmode 'VHT80'
If I use HT40, I manage to get 200mbps, VHT80 should be supported, but by some reason it is causing issues. My phone probably doesn't support MIMO, that was the difference in speed with my laptop.
Any idea on how to fix the incorrect phy info? This device supports MIMO 4x4...
I followed this discussion prior to installing OpenWrt:
https://forum.openwrt.org/t/netgear-wac124-mediatek-mt7621at-support/37959/19
Maybe @janh or @patricius could help me?