Audio Systems: Audio; phone; speaker, rca jacks, phone handset

Question
First of all, thank you for even reading this.  Here's my situation. I have an elderly, disabled, hard of hearing friend.  I need to set her up with a telephone (landline).  It has to be set up so she doesn't have to pick up the handset.  It has to be a speakerphone. Loud.  No, actually LOUD!!! I tried all the crappy specialty phones for hard of hearing people.  Not even close to loud enough.  (She's almost deaf).
So I want to connect the phone audio to a stereo, and crank it up. I Hooked the phone base headset jack (3.5mm female) to an adapter to the red/white RCA jacks on the stereo.  It works, but not how I need it to.

Setup #1: Plugged into the video input on the receiver:
It is not nearly loud enough, and when I turn the volume past 50%, I get major high-pitched feedback.  It is like its not amplifying the power enough or clearly.  The stereo (receiver) is kinda old, but works just fine, and is attached to fairly powerful speakers.

Setup #2: Plugged into the phono input on the receiver:
It's plenty loud.  But there is tons of bass.  Waaaaay too much bass.  If I turn the volume up past 25%, my whole house thumps.  I turned the bass down, the treble up, I adjusted my equalizer all the way, and it's still too much.  Whenever I pick up the phone handset, there's a ton of background bass too.  I feel like I'm almost there- if I could turn it up to 40% with way less bass, it would be enough for her to hear clearly.

Do you know what I need to do differently? (without breaking the bank)? adapter/simple amplifier/etc.

Again, thank you for your time,
Bill


Answer
ONE: Can't use the video input

TWO: Can't use a phono input

THREE: Must use an audio or aux input.  It is mono signal.  You don't need stereo.

FOUR:  If you turn it up too far you will get acoustic feedback.

FIVE:  There is no way to avoid the feedback unless you use earphones.

If you want to keep feedback to a minimum you may need to move them further away from the phone and aim them away.  Give it a try and see how strong it will go, but you will always face feedback with strong output coming from the speakers  -  unless you purchase professional telephone equipment like they use in broadcasting which has delay and echo cancellors.


Hope this helps.
C