A real Wi-Fi signal booster is a cooking pot lid, like these:
View attachment 54981
(A mesh stainer instead of a lid can also work, by some accounts better)
Simply keep the smartphone (antenna) in the focal point of the lid and point the lid, in the same manner as a parabolic antenna, toward the Wi-Fi router.
The lid increases the strength of the Wi-Fi signal usually with 1 gradation which you can easily check on the screen of you phone.
I know this trick it is not quite practical but in some situation can save you.