To me, it IS controlling if you are just establishing different rules than W and not discussing with her. I think it’s reasonable to discuss the phone usage expectation with w rather than just “taking it” from your kids. W have it to them to use at your house to talk with her. So you taking it is changing her rule through them rather than being united with her about the expectations. You shouldn’t be communicating these kinds of decisions through the kids if your expectations differ from w’s.

When the kids have/had free reign with the phone at your house, did you cap time with it? Did you set rules/guidelines/expectations? Or is it YOU who is doling it out like a gatekeeper?