The Nintendo Voice App has by far been the most outdated and ridiculous peripheral Nintendo has launched to date, but they did fix recently to make it a little less garbage. The latest firmware update for the voice chat app now allows players to continue chatting with their friends when their phone is locked as well as when they open other apps.
While this new feature will work with most iPhones and Androids there is a note that those who have Android 6 or later will not be able to use this feature if they have power saving mode activated.
Of course, the best fix for the app would be to make it available on the Switch and just drop the whole smartphone nonsense out of the equation completely. Apparently, that's too much to ask. It's a good thing I don't enjoy online chat anyway!