That's the point though. The address is randomized per connection specifically so the device can't be identified. It's to prevent tracking, blocking, or assigning, anything based on mac address without the device owners knowledge. Every time your phone connects the network has to treat it like a new device. If it was randomized per network that would defeat the point.

I personally can't think of any reason you would need a static IP on your phone but if you did then you should know enough to know how to turn off the randomized mac address. You can even change the setting per network so if you need a static ip at home then you just set your phone to use a static mac address on your home network and continue using a randomized one on every other network.