Problem solved: The external sound switch (near the volume up/down buttons) had flipped to off when I removed or re-installed the drop protection case. Why it affected only games seems strange.

After replacing the battery, the audio from games is not audible over speaker. All other apps using the speaker seem to work: Phone, Clock (alarm), FaceTime, Skype, and YouTube are all audible. Could the issue with games be caused a poor seating of any of the connectors detached and re-attached in the battery replacement process?

My iPhone 6 is three years old. GPS became unreliable a few months ago. I decided to buy an iPhone 8 Plus and replace the antenna cable and battery at the same time. The procedure took about 3 hours while I watched football. The hardest part was getting the existing battery out because the tape broke when I pulled it. A heat gun helped to get the adhesive pliable. Now my daughter has a “new” phone. Thanks for this guide!

I broke two of the connectors on the existing antenna cable, but the connectors on the board remained intact. The new cable attached with no problem for me.