Thank you guys for the quick reply!
I could eliminate de bluetooth for the moment. The audio input is a landline phone call. I don't really need a good-quality audio (just comprehensible) . My idea was to connect the RJ11 to an adapter from RJ11 to jack. Then i would connect a wire ( i ve seen on youtube that i can put one end of the wire on the top of the jack and the other one in analog 0 of arduino and it will receive the audio).
From here i could change the project to only output the audio through some speakers. Should i analogWrite() on a pin where i would connect the speakers?