Landline phone question?

We have a landline phone. Our cordless phones and wired phones work perfectly in the house. However On some specific numbers, the cordless phones receives them terrible while the corded phones receives them perfect. The cordless phones in our house are like this, one as the base hooked up to the telephone line... show more We have a landline phone. Our cordless phones and wired phones work perfectly in the house.

However

On some specific numbers, the cordless phones receives them terrible while the corded phones receives them perfect.

The cordless phones in our house are like this, one as the base hooked up to the telephone line while the others connected to that base.

What could this be caused from?
Update: The cordless phones are new, DECT 6
The phone numbers on both the cordless and corded phones comes in great, some specific numbers however, only the corded phones receives them really good, and you can barely hear them over the cordless phones and a lot of static.
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