Default WiFi network

If you are going to have two different networks closeby, the iPhone is not going to make a choice based on network speed. It will make the choice based on strength. If you wish to make sure it connects to a specific network, you are going to have to forget the other network. There is no way to prioritize connection on the iPhone like there is your Mac.

Because that is the way that it is configured. You can ask Apple about it if you wish. Use the Contact Support link at the top of the page. The iPhone does not have a wireless network configuration setting like the Mac computer does, so there is no way to prioritize which network it connects to. Then, the only way to get it to connect to the fastest one would be to have to pre-test the network, which I'm not aware of anything that does that. You could always set the networks to ask to join, so you could select the one you want, but that is not going to get you the information about the fastest network, just the one with the best signal.