The difference in speeds can be explained by the fact that LTE cat4 modems are not capable of carrier aggregation, which would be a significant factor in regards to increased performance. Your iphone and android devices might also employ some form or MIMO and other advanced signal processing techniques, missing in TRB245.
I would suggest to try setting custom LTE bands, to look for possible improvements. You can do it in the WebUI, by going to Network -> Mobile -> General section and switching to Manual option of Band selection setting. A different antenna can also be tested.