touch screen not working in phone app after screen replacement

I recently replaced the touch screen on my iphone 6. The replacement went off without a hitch and when I restarted my iPhone everything appeared to be working fine. I was able to use all my apps, surf the web and place a phone call. However, when I attempted to engage speaker mode the options appeared and the the screen went blank, however, my phone call stayed connected. When I pressed the Home button the options screen appeared for a second and then went black. Next when I tried to hang up the phone conversation the dialer screen appeared but the disconnect button did not function and the screen went black. The only way to disconnect the phone conversation was to perform a hard shutdown. When I rebooted the phone everything appeared normal and I was able to call another phone, however, once the call is initiated the touch screen becomes unresponsive and turns off after a second. Touching the Home button displays the screen data but the screen goes black almost immediately. When the call is terminated the screen works perfectly.