Different speeds for mobile phone vs 4g router with same sim

I'm using a Smarty sim in my phone and getting 40-50mb/s but when I transfer the same sim, in the same spot in my house, I then only get 5-10mb/s.

Google Pixel 6 / Huawei 4g router B535 (previously bought via Three)

Does Smarty throttle connection when not used in a handset?

Thanks!