Diagnosis
You're stuck in the middle of the setup process. The pulsing white light means it's in 'ready to pair' mode, but the Google Home app on your phone has lost the connection or can't see it.
How to Fix It
First, force close the Google Home app completely on your phone. Then, unplug the router from power for a full 30 seconds and plug it back in. When the light starts pulsing white again, open the Home app and tap the big '+' to add a new device. It should pop up. If it asks for a QR code, look on the bottom of the router itself.
If That Didn't Work
The phone's Bluetooth might be interfering. Go into your phone's settings and turn Bluetooth off completely, then restart the Home app and try the setup process again. The Nest Wifi Pro uses a Bluetooth handshake initially, and sometimes other Bluetooth connections can gum it up.
Heads Up
During setup, keep your phone within a few feet of the router. It's not using WiFi yet, so being too far away can break that initial Bluetooth connection it needs to get started.