Testing cellphone speakers out of circuit
A simple way to do a good/bad test on a speaker is with a 1.5 V battery and a 100 &Omega; resistor in series.  If the speaker is working, you will hear clicks as the connection is made and broken.

Instead of a battery, you can use a bench supply, like 5 V.  In that case use 300-500 &Omega;.  The point of the resistor is to limit the current to 10-15 mA.  That should be enough to cause something audible, but below what could damage even a small speaker.