You can do it for TV antennas.. but there isn’t a lot of benefit to combining cellular antennas. If you are getting any signal at all, putting up a larger-sized cellular antenna on your roof and using an appropriate cell booster will help you get the reception you want indoors. If you’re not getting any cell signal at all, combining multiple antennas probably isn’t going to help.
The best thing you can do if you’re having reception problems is put that antenna up as high as possible. Get it past the trees and homes that might be blocking the signal and it should work well for you.