have you tried a factory reset?
Thank you, ocnbrze - factory reset worked! As my girlfriend pointed out, I'd bought this new phone after having the other one for 3 years (I dropped it and it shattered and fixing it would cost almost as much as buying a new phone) and transferring all the info off the old phone meant I had a few apps that needed to be updated.
So when I did the factory reset, I answered "Yes" to updating all apps, and now the phone shows me my arrows so I can close out of apps and go "home." Case closed.
Another thing my girlfriend pointed out is that phones for sale at a retail store may have sat there on display and in stock for over a year, meaning that when you activate the phone, you should make sure all apps have the most current version, so don't transfer, say, Instagram and Snapchat as they were - install new versions and sign in.
Cheers and best to all.