I have also been looking for a solution that doesn't rely on wifi (internet) and like you also realized our phone is (sadly) not capable of a plugged in solution (which would be ideal).
I found this (
https://www.amazon.com/gp/product/B...ag=hawk-future-20&ascsubtag=UUacUvbUpU5375978 has a micro USB port for powering the device and on my t.v. I have a regular USB input port so I can plug the dongle into the television HDMI port and a micro USB to regular USB power cord into the television USB port. The package comes with a micro to regular USB cord AND the wall plug-in brick if you don't have a USB port on your television...in other words you should be able to use it straight out of the package so long has you have an open HDMI port.
I have not played with it extensively but used it at a friend's house who has NO wifi at all (no internet, no cable). I plugged the dongle into the HDMI port on the t.v. and the USB charging cable into the USB port on his t.v., went into the settings on my phone and turned on "SmartView" and bingo...they connected and my phone was mirrored on the television. I had a movie on my memory card in my device and streamed that to his television (use your player of choice since it's mirrored). The broadcast was as smooth and as HD as the original recording was, however I noticed the sound cut out at times...not quickly, but for several seconds at a time (so not just a word here and there , but it would go out entirely for many seconds). We didn't try to actually watch the movie...I was more or less playing around with it. I also fired up Netflix and was able to stream that to the television but again, I didn't spend a lot of time with this setup so I don't know if the sound would be an issue there or not. I'd like to think maybe my movie was just wonky but I've watched that movie before with no issues (NOT streaming). I'm not sure if LTE data is being used with this setup or not...they are supposed to have a wireless "direct" connection but I doubt they are doing it without data of some kind. My friend's house is not in the best reception area... -110 on average for signal.
I did read the dongle gets very hot...and I can confirm this. I don't know if it's too much for the t.v. to handle for a movie or two or three, but I would definitely not leave it plugged in indefinitely.
I hope this helps. Also, I'm sure the ScreenBeam Mini 2 isn't the only dongle out there that has a separate power port. Admittedly I don't know much about HDMI or whether it's even supposed to be capable of powering a device so maybe they ALL have some type of charging port. Or maybe this is the only one that does...not sure.
ETA: I just looked at the dongle the prior poster provided and it is powered the same way the one I linked to is. That is, with a micro to regular USB cord and with a wall brick you don't need to have a USB port on your actual television.