Poor cell reception compared to others in same house

My family is on the same phone plan and my phone (iPhone 8) has significantly less reception than others in the same house — even when our phones are side-by-side. My phone will toggle between ‘no service’ and one bar, whereas another phone (ie, iPhone SE) will have 3-4 bars and our phones are right next to each other.

I have read another thread on this subject which didn’t apply to me — that article mentioned a specific phone case (‘with metal’) that was possibly blocking service. I can’t imagine there is anything physically blocking my reception— I have a very basic plastic phone case.

Any ideas as to the cause - and solution - of this would be greatly appreciated. Thank you very much.