Landline out signal amp

People I call on my landline say “Speak louder.” I can hear them just fine. I have no cell phone, but I do have a cordless phone and a cord phone. My house has 1930’s two-wire phone lines in the walls that lead to my cable company’s modem. When I plug my corded phone directly into the modem, people I call can hear me fine, so the signal reduction is in the old wiring in the walls. I can fix that, or buy an off the shelf signal amp to insert between the modem and the poor in-wall wiring.

There are many amps designed for me to hear better, but I already hear just fine. The boost needs to be on the signal OUT, and not the signal in. Can you recommend a signal out amp? Thanks.

If the wiring really is the problem, and you can replace it, that is by far the best solution.