There are some connections for the earpiece speaker that can be a little tricky to get properly connected during reassembly. If you look at the third photo in step 22 of the iPhone 7 Plus teardown you can see four copper pads on the cable, and four protruding copper connections on the speaker. For starters, make sure that these are all clean. When reassembling, make sure that the metal pads on the cable firmly touch the metal pins on the speaker. These are actually electrical connections, and are a little tougher to seat properly because they don't snap in like press or ZIF connectors. If the metal is all lined up and pressed against each other, then electricity should be flowing and sound should result! If the earpiece speaker was not removed and this guide was followed as is, it is most likely an issue with the connectors in step 19 of this guide.