Wireless Joint

Your numbers look pretty good not sure if an attendance going to help.

Your modem is a Cat-7, your phone is most likely a Cat~20+. Not fair to compare the two.

Make sure to use a hard Internet cable connection for your speed test. This would remove WiFi from the equation.

Is there a way to tell what bands your modem is connecting to?

Cell mapper is a good staring point but is often outdated information .

Most cheaper modems do not have

Carrier Aggregation & MiMo which are helpful for better speed.

https://www.cashify.in/what-is-carrier-aggregation-how-can-it ...

A good test to see if an antenna will help is bring your modem to the cell tower for a speed test.

Use a good quality power inverter or better use 12v from a vehicle if you have access to one.

This would give you a baseline of what speed is possible with a good signal.

Keep an eye on your signal ...

Here's what I get

Here's my setup in the attic

If you do not have whips or paddles already you can start with those. Since you mentioned being in another country it would be hard to recommend any but I am sure an Internet search would turn some up. You could look at this Forums merchant website for ideas of types.

Also would recommend these

I have 2 of these as u can see in the picture. and recommend buying these

I have 2 em20-g modems on Firstnet one ca on band 14 and 2 and the other on band 2 and 29