My transitor amplifier is deamplifying
The output impedance of a phone is &lt;10 ohms (it easily drives 8 ohm earbuds), so you're increasing the output impedance with your "amplifier": At the beginning, you bias it using a voltage divider with impedance of around 2kOhms, then at the end of the circuit your amplifier is based on a 4.7kOhm resistor, so it has output impedance of 4.7kOhms.  If you're driving a 4 ohm speaker, you have far too high output impedance.