Hello,
To start with, regarding your mobile speeds, you can try to move router's position closer to the window or have wired mobile antenna and place it in higher location with hopes to acquire better signal reception. That might improve router's performance.
Additionally, from configuration side you can try to force router to different LTE bands in the area and then check what speeds you are getting when router is connected only to specific LTE band (In your area there could be multiple LTE bands available, while router might be prioritizing only one of them. Forcing device to use another band might increase the performance. To know for certain actual test would need to be made in your location). You can also check your mobile phone's settings and try to find to what LTE band it connects and then use same band on the router.
Meanwhile, regarding your finding that your mobile phone is achieving better mobile speeds - that is often the case due to simply fact, that mobile phones have higher LTE category LTE modules, which allows to use multiple LTE bands simultaneously. We have article briefly explaining why such speed difference between different devices might be encountered. Article can be found here: https://wiki.teltonika-networks.com/view/LTE_Speed_Discrepancies
Lastly regarding your "TP link boosters", unfortunately, I would not be able to comment why your TP link devices are not working as expected. I could only suggest to first make sure that stable/fast internet connection reaches your TP link device, since one possibility is that issues might be related with poor connection which TP link devices receive. If that would not be the case, then it might be configuration related.
