they don't understand something, i will repeat and i don't care if anyone of these brains pays attention,
mobile phone works on 3.6V, if the speaker is 8ohm (i think it's more), the max power is U/R=I P=U*I so 3.6/8=0.45A P=0.45*3.6 P=1.62W, and 1.62W is the peak power, if you want more then amp gets into saturation U=Max so the direct curret runs through the speaker