No gyms required here. You just check by looking at how many signal bars there are. The signal strength icon is on the top right corner of your phone. The horizontal bars represent the strength of your current connection; the more filled bars the stronger the signal. You might also see the letters “3G" "4G" "LTE" or "5G." The strength of the signal is in that order with 5G being the highest. If your phone uses iOS, open your Control Centre to see in more detail.