wireless client bridge connection to mobile phone hotspot

1. The desktop has Ethernet but not Wi-Fi.
2. I have a router set up as a wireless client bridge.
3. That connects the desktop to the home router access point.

But... 

I can't get the same desktop to work with the mobile phone access point.
A. I turn on the mobile phone access point on the phone
B. A laptop with Wi-Fi can easily connect to that mobile phone AP
C. But the router as a wireless bridge cannot establish the connection

Why?