1. You are making the ethernet connection to the LAN port, not the WAN port, yes?
  2. Under More Settings|Network Mode, this is set to “Router”, yes?
  3. You are trying to connect to the EE Mifi under Internet|Repeater|Scan, yes?
  4. You can still try with the phone, temporarily disabling the other networks. I have no difficulty connecting wirelessly to my Beryl and then setting up the connection to another wifi network. Quite reliable for me.

PS: The Beryl and luci is OpenWRT, not DD-WRT