Will moving the sim card from the phone to the router improve the quality of the

Hey, So far, I've been using mobile internet on my phone for about a year. I made a Wifi router out of it and it was enough for all the devices in the house. Internet quality has dropped drastically over the last few weeks. I suspect it has to do with the quarantine and everyone in the area is staying at home and using the internet as much as possible.
Therefore, I was thinking about buying a modem that supports sim cards. After all, this is equipment dedicated to splitting the signal into several devices. Unlike a phone that has this option but is not for that.

My questions however are:

Will investing in such a router help to solve at least partially problems with internet speed? I mean, will moving the sim card from the phone to the router significantly affect the connection between the card and the pole it connects to? Theoretically, it should, because a lot depends on the device in which it is located. I'd love to get advice from someone who knows more about these issues.

I don't know if it makes sense to invest in a router in this case. Is the only option to wait for a return to normality when not everyone will be sitting at home and using the internet at the same time?

Thanks in advance for your interest.

How's the location, what operator?

I live in the British Isles currently. My question was rather purely theoretical because I knew that I couldn't give a location in Poland.

I will give my place of residence as a rule, but you probably asked the question with Poland in mind.

Three UK and West Midlands.

I asked about the location because you have to take into account the signal strength that reaches you, i.e. the distance from the transmitters, etc.
It is known that the phone has a poor antenna and inside the building the signal is attenuated and susceptible to interference.
A router with an external antenna has more possibilities.

As far as I can tell you, a few weeks ago, despite the fact that the phone is old, the network coverage was at 75% practically all the time in the place where it was lying.

Now it jumps between 25 - 50 looking at the number of range bars. I read in one article that the more devices connected to one transmitting mast, the more its signal transmission power decreases. Totally logical.

I'll try to borrow a router from someone who has this type of router and see if it changes anything.

It would be best to have cable internet, but in this situation I will not be able to arrange it anywhere and additionally technicians will defend themselves with their hands and feet before the visit.

Purely theoretically, this should improve the connection.

Thanks anyway.

Install the NetMonster program on your phone and give a screen with the frequencies used.
Also show the result from Network Cell Info from the Indicator and Data tabs.
What are your current UL/DL speeds?
What (which) category do you have a modem on your phone?