Can't hear from landline

I have a Uniden fp 1100 handset.

When people call me, I answer and I can hear them and they can hear me.

When other people call me I can not hear them at all, I am unaware of they can hear me.

It appears to me that the people that I can't hear are also using a landline as well, would this have anything to do with this problem.

Thanks for your help.

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What happens when you call a person in each group you’ve identified? Are you able to have a dialog with each and when they call you back after you’ve called them are they still failing where you expect?

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