To get my helpline of my escape room working I'm trying to install a miniature speaker in the horn of an old phone.

I have bought this speaker

Miniatuurluidspreker KP-serie Geluidsontwikkeling: 90 dB ± 3 dB 8 Ω Nominale belastbaarheid: 0.8 W 650 Hz ± 20 % Inhoud: in de Conrad online shop | 710982

When I solder the speaker on a minijack and connect it to my iphone, I get a decent but a little bit to quiet sound. When I use the real setup (speaker connected in phone - phone i wire (which is replaced by an utp cable of a necessary 10 meters) connected to my iphone the music plays, but the voice frequencies are very distant and almost inhearable. When I try to amp the volume by connecting to an old stereo amplifier I get very much distortion and now I fear I destroyed the speaker.

Can anybody help me with this setup ? do I need an other speaker? what can I use to amp this speaker? does the long way of utp cable create a problem ?

any help is welcome