So, if my phone is near the router, so that said - on my PC, the wifi signal is very good, but if I decide to go to the kitchen, which is 5-10 steps further the wifi drops very fast, even the connection is lost.
Which frequency you are talking about:
2.4Ghz : interference --> real issue on 2.4G, If you have lot of neighbours this kills range...
5Ghz, older devices/phones have pretty bad 5GHz performance. Newer smart phones have 2x2 5Ghz Wifi which is providing better coverage.
With that 5Ghz should still reach across one concrete wall at least.
Then what AP are you using? 4x4 5GHz does better than 2x2 or just 1x1 .. clear with a hap ac lite your 5G range will be very limited.
Im using hAP ac². That being said im using an Huawei P20 lite and yes, there's only one concrete wall between my room and the kitchen. Previously i used an old tplink 940nd and i didn't have any issues like that.