Most smartphones released after year 2015 are using 2x2 SU-MIMO chip already except those low end smartphones. Flagship smartphones released after year 2016 (e.g: Samsung Galaxy S7) are using 2x2 MU-MIMO chip (802.11ac Wave 2) most of them are powered by the Wi-Fi leader + hegemon Broadcom (Broadcom Numba Wan).

But in recent years still have some guilty smartphone vendors use 802.11n single-band 1x1 chip on their low end smartphones to cut cost + clear inventory like Huawei Nova 3i (2018), Huawei Y5 (2019), Redmi 7 (2019), Realme 3 (2019), Realme C2 (2019), Samsung Galaxy A10 (2019), Samsung Galaxy A20 (2019).

TP-Link a freaking networking company usually will also use their old inventory of 802.11n chips on their low end smartphones like Neffos C9 and Neffos C7. Well at least TP-Link did put a 802.11n dual-band chip into their mid range smartphones like the Neffos Y7. 802.11n dual-band chips were very popular among flagship smartphones around year 2011-2013 before smartphone vendors adopt the 802.11ac Wi-Fi standard, most notably used by the original iPad (2010), iPad 2 (2011), Samsung Galaxy S2 (2011), Samsung Galaxy Nexus (2011), HTC Amaze 4G (2011). Yes they all have 802.11n dual-band Wi-Fi.

Smartphones released before 2013 are using 1x1 SU-MIMO for example that flagship Samsung Galaxy S4, if it's 802.11n then the max data rate on 5 GHz is 150 Mbps, if it's 802.11ac like the one can be found on HTC One M7 (2013) then the max data rate on 5 GHz is 433.3 Mbps. FYI HTC One M7 is actually the first smartphone with a 802.11ac chip powered by Broadcom Wi-Fi + Bluetooth + FM radio combo chip all the way back in 2013.

It's 2019 but so far no smartphone on earth comes with 3x3 MU-MIMO radio yet.