One can use fixed LTE in a 4g enabled phone. The compatible device list is what their helpdesk is trained to support.
If there isn't a tower near you, the router/phone will move from tower to tower looking for a better signal. It can do this every few seconds. The upload/download discrepancy is (IME) normal for this scenario.
We had 25mbps on our Fixed LTE using a phone, then the tower near us went down and we ended up with exactly the same symptoms you're having - we're with Afrihost using Telkom LTE. We reported it to Afrihost and Telkom sent a techy a week later. It took about 2 weeks after that for the tower to come back up. Eish, this was a day before the latest international cable break.
It could be you're in a bad location where there is LTE, but no tower is the clear winner, or the best tower for you is down - apparently some of them don't come back up after loadshedding, and Telkom doesn't have an automated notification system to help them spot down towers; they rely on problems being reported. Put card in phone and hunt around house and garden for 3 bars of 4g LTE signal - or stable 2 bars if that's all you can get. I found 3 bars by perching my phone on top of our washing line, which is where we left it for the duration of the issue. I put it in a big box inside a garbage bag, fed a power cable through an open window to keep it charged. It stayed there day and night till the tower came back up. Connection dropped out occasionally, but we got 1.5mbps to 5mbps or so.
I did get a Huawei b315s, but it worked only marginally better than my phone and ipad.
Report it to Vox.
I doubt it's the router, but try your phone and if the same problem exists, it's not the router. I went through the same supported router marlarkey with Afrihost, so I borrowed a b315s to test and help their helpdesk grasp the issue. I ended up buying it, but in my view unnecessarily.
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