Ubiquiti Networks UAP-AC-PRO
You should be able to link up at 867Mb/s. Since that's both ways, you'll get roughly half that in real world when downloading or uploading. Figure slightly less than 400Mb/s each way.
You can try to upgrade your AC Pro firmware and see if that helps. Also do the following in your controller:
Upgrade to 5.9.32 or higher.
Enable advanced features
Don't use airtime fairness or band steering in AC Pro device settings. To force 5Ghz set a separate SSID and assign only 5Ghz radio.
Make sure 5Ghz radio is set to 80Mhz
For WiFi networks use WPA2 AES only.
Turn off connectivity monitor.
Disable unscheduled auto power save delivery
Do you have another router or using the isp modem as a router?
FYI, your AC Pro is capable of 1300Mb/s link with about 600Mb/s each way. Your phone isn't.