If your phone is not on airplane mode, then the device is constantly transmitting it's unique identifier (IMEI), time, and location, regardless of the sim.

So if anyone with that data (literally anyone, as it can be bought on darknet) wants to track an individual, just catch that person on a camera, and triangulate with the IMEIs in that location at that time. It will only take a few recordings to find the IMEI, and boom, you can now track that person anywhere (follow the IMEI). Every sim card you put in that phone can be reasonably associated with the owner of the device (because when you use the sim, you transmit both the IMEI and the IMSI / sim identifier).

My recommendation would be to purchase a GL 750 travel router (mudi) and install Blue Merle software (2 commands).

You can then switch the IMEI every time you switch the sim (ie, monthly) so the most you would typically reveal would be a months worth of tracking data.

Also, 100% of your traffic will be over VPN so the provider will know nothing about your browsing habits / destinations. And Blue Merle will also wipe the connection logs from the router.

Alternatively, just buy a cheap dongle and throw it away. The downside is, you won't have any VPN on the dongle, so you better hope your phone isn't leaking outside the VPN (Apple is guilty of this)