[bblough]

The cordless phone system I have lets you make/receive calls via your cell phone from any handset in the house. It connects via Bluetooth, so isn't a dock, but the functionality is similar to what you're suggesting.

Mine is an older Panasonic system, but I'd be surprised if other manufacturers didn't offer something similar.

[rubidium]

Like this? https://shop.panasonic.com/cordless-corded-telephones/cordle...

[bblough]

Yes, mine is very similar.

Though, (and I should have mentioned this in my original comment, sorry) I've never actually used the functionality in question, so I don't know how well it actually works.