Why does Wi-Fi practically stop working on phones?

Question

WiFi

Good day.
There is a router that distributes Wi-Fi, a PC is also connected to it via Ethernet, but for some reason, going down to the floor below Wi-Fi stops catching normally only on phones, everything is fine on a laptop, everything works fine via Ethernet too. The problem appeared simply because of nothing, literally a month ago everything was fine, everything worked.
Router: zyxel keenetic omni
did not go into the settings, did not change anything

Answer 1

Radiation pattern for reliable reception from a whip antenna router. Just place one/two antennas horizontally. It is necessary that the perpendicular line to the antenna pin pass through the point on the floor where you want a reliable reception.
If the antenna is not removable, then it will not be possible to extend it.
And yes, download something like Wi-fi Analyzer and show what Wi-Fi is at the point on the bottom floor.