How can I convert an audio signal from a phone to 0-5v for a microcontroller?
This circuit, a non-inverting summing amplifier, can be used for your purpose.



The left op-amp is a 2.5v voltage reference (derived from your 5v supply), and the right op-amp is the summing amp.  With the values shown, it takes the ±2.5v Audio input and adds it to the 2.5v offset, resulting in a 0-5v output.

If R3 = R4, then Output = Gain * (Audio + Ref) / 2
Gain = (R5 / R4) + 1 = (49.9K/49.9K) + 1 = 2
so Output = 2 * (Audio + Ref) / 2 = Audio + Ref.