Like Just_Me_D said contact your service provider they can usually hook you up with a booster for your house. Or you can buy a booster from amazon and install it yourself. We have one at our job site and it is literally in the middle of nowhere. No building or humans for 30 miles. The booster we have gives us 2-3 bars of LTE.
I also have wifi calling enabled in my iPhone so I can make calls using wifi