OnePlus' newest flagship device, the OnePlus 5, has some strange issues with installations of Google Dialer and Google Contacts that are done through the Play Store, but XDA Developers user dustintinsley has created a flashable Magisk module to solve the problem. Usually, installing those apps through normal means would result in being unable to answer or decline phone calls through the notification pop-up. By flashing this module and doing a little bit of permission and default app tweaking in the phone's settings, Google Dialer and Google Contacts will work as intended. There is even a TWRP-flashable version that doesn't depend on Magisk for those who don't want to take the plunge with writing to their boot partition, and an installer script to make things as easy as possible.
The procedure itself is relatively simple; start by installing Google Dialer and Google Contacts from the Play Store, if you haven't already. From there, as long as you have either TWRP or Magisk, just flash the module found in the first post through the source link. If you use the Magisk version, be sure to enable the module, then reboot the device. Once the module is fully in place, go into your app settings and disable the default OnePlus dialer, then approve all permissions for Google's version, and make it the default. From there, it should be fully functional with no issues.
Although there is a preliminary version of the Xposed Framework for devices running Android 7.0 Nougat, it's far from stable at the moment. This means that Magisk's module functionality is a real lifesaver for power users who like to customize core device functions, but also like to run the latest available version of Android. While Magisk's ecosystem is not quite as full-featured as that of Xposed, a large number of modules have been ported over, or even created specifically for Magisk, making it a fairly robust solution for those who can't use Xposed for one reason or another. Magisk Modules, just like Xposed Modules, are simply system tweaks running on a framework, so in many cases, it's possible to create TWRP-flashable versions or install scripts, as has been done here.