Even if it's ideal miles is shouldn't be that drastic of a difference in charge rate, especially at 7 amps. At 7 amps, 110v single phase it should only be charging at 2 or 3 mi/hr. You'd need to be pulling 3Kw to be able to get up to 8 mi/hr and three phase at 7 amps would be that exact amount.
Bigger question is that I don't think the mobile charger can handle three phase power, so that's a mystery... in addition to how you'd be getting three phase power on a 120 outlet with only one hot wire. Gremlins?
Ok so I was right. The rates are at rated not ideal. When I changed to ideal it jumped up to 9/10mph