Wi-Fi amplifier interferes with your own internet?

I connected my ps4 to an amplifier and it works great too.
in another room there's an amplifier that also works great.

Now comes what I do not understand, my cell phone only gets Internet via the two routers, but if I connect directly to the in-house Wi-Fi and stay near one of the amplifiers, I get no connection.
Does the amplifier interfere with my cell phone? Or the Wi-Fi itself?

For me it is not so repeater

Yes, it wasn't really like that since I started running the 2nd

Make sure that they don't have the same SSID, that solved it for me

You have to disconnect from the router and manually connect to the repeater. These repeaters in combination with mobile devices are not particularly smart, so you have to make sure that you are connected to the correct "WLAN".

As already written below, the repeaters should have a different SSID for better differentiation.